A National Survey of Methyl tert-Butyl Ether

and Other Volatile Organic Compounds in

Drinking-Water Sources:

Results of the Random Survey

Water-Resources Investigations Report 02-4079

U.S. Department of the Interior

U.S. Geological Survey

NATIONAL WATER-QUALITY ASSESSMENT PROGRAM

NATIONAL SYNTHESIS ON VOLATILE ORGANIC COMPOUNDS

Prepared in cooperation with the Metropolitan Water District of Southern California,

the Oregon Health & Science University, and the

American Water Works Association Research Foundation
U.S. Department of the Interior

U.S. Geological Survey

A National Survey of Methyl tert-Butyl Ether

and Other Volatile Organic Compounds in

Drinking-Water Sources: Results of the

Random Survey

By Stephen J. Grady

Water-Resources Investigations Report 02-4079

Prepared in cooperation with the Metropolitan Water District of Southern California,

the Oregon Health & Science University, and the

American Water Works Association Research Foundation
U.S. Department of the Interior

GALE A. NORTON, Secretary

U.S. Geological Survey

Charles G. Groat, Director

The use of firm, trade, and brand names in this report is for identification purposes only and

does not constitute endorsement by the U.S. Government.

East Hartford, Connecticut: 2003

For additional information write to:

District Chief

U.S. Geological Survey

101 Pitkin Street

East Hartford, CT 06108

http://ct.water.usgs.gov

Copies of this report can be purchased from:

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Information Services

Building 810

Box 25286, Federal Center

Denver, CO 80225-0286
Foreword III

FOREWORD

The U.S. Geological Survey (USGS) is 

committed to providing the Nation with accurate and 

timely scientific information that helps enhance and 

protect the overall quality of life and that facilitates 

effective management of water, biological, energy, and 

mineral resources (http://www.usgs.gov/). Information 

on the quality of the Nation’s water resources is 

critical to assuring the long-term availability of water 

that is safe for drinking and recreation and suitable for 

industry, irrigation, and habitat for fish and wildlife. 

Population growth and increasing demands for 

multiple water uses make water availability, now 

measured in terms of quantity and quality, even more 

essential to the long-term sustainability of our 

communities and ecosystems.

The USGS implemented the National WaterQuality Assessment (NAWQA) Program in 1991 to 

support national, regional, and local information needs 

and decisions related to water-quality management 

and policy (http://water.usgs.gov/nawqa). Shaped by 

and coordinated with ongoing efforts of other Federal, 

State, and local agencies, the NAWQA Program is 

designed to answer: What is the condition of our 

Nation’s streams and ground water? How are the 

conditions changing over time? How do natural 

features and human activities affect the quality of 

streams and ground water, and where are those effects 

most pronounced? By combining information on 

water chemistry, physical characteristics, stream 

habitat, and aquatic life, the NAWQA Program aims to 

provide science-based insights for current and 

emerging water issues and priorities. 

From 1991-2001, the NAWQA Program 

completed interdisciplinary assessments in 51 of the 

Nation’s major river basins and aquifer systems, 

referred to as Study Units (http://water.usgs.gov/ 

nawqa/studyu.html). Baseline conditions were 

established for comparison to future assessments, and 

long-term monitoring was initiated in many of the 

basins. During the next decade, 42 of the 51 Study 

Units will be reassessed so that 10 years of 

comparable monitoring data will be available to 

determine trends at many of the Nation’s streams and 

aquifers. The next 10 years of study also will fill in 

critical gaps in characterizing water-quality 

conditions, enhance understanding of factors that 

affect water quality, and establish links between 

sources of contaminants, the transport of those 

contaminants through the hydrologic system, and the 

potential effects of contaminants on humans and 

aquatic ecosystems.

The USGS aims to disseminate credible, timely, 

and relevant science information to inform practical 

and effective water-resource management and 

strategies that protect and restore water quality. We 

hope this NAWQA publication will provide you with 

insights and information to meet your needs, and will 

foster increased citizen awareness and involvement in 

the protection and restoration of our Nation’s waters. 

The USGS recognizes that a national 

assessment by a single program cannot address all 

water-resource issues of interest. External 

coordination at all levels is critical for a fully 

integrated understanding of watersheds and for costeffective management, regulation, and conservation of 

our Nation’s water resources. The NAWQA Program, 

therefore, depends on advice and information from 

other agencies—Federal, State, interstate, Tribal, and 

local—as well as nongovernmental organizations, 

industry, academia, and other stakeholder groups. 

Your assistance and suggestions are greatly 

appreciated.

Robert M. Hirsch

Associate Director for Water

Contents V

CONTENTS

Abstract.................................................................................................................................................................................. 1

Introduction ........................................................................................................................................................................... 2

Purpose and Scope....................................................................................................................................................... 3

Acknowledgments ....................................................................................................................................................... 3

Implementation of the Random Survey................................................................................................................................. 4

Geographic Distribution of Participating Community Water Systems........................................................................ 5

Temporal Distribution of Source-Water Samples........................................................................................................ 9

Data Collection and Analysis ................................................................................................................................................ 10

Collection of Source-Water and Quality-Control Samples ......................................................................................... 10

Analysis of Data .......................................................................................................................................................... 11

Review of Field Quality-Control Data......................................................................................................................... 14

Collection of Ancillary Information ............................................................................................................................ 25

Occurrence and Distribution of Volatile Organic Compounds in Drinking-Water Sources.................................................. 26

Comparison by Type of Source Water and Size of Community Water System........................................................... 29

Trihalomethane Disinfection By-Products ........................................................................................................ 32

MTBE and Other Gasoline Compounds............................................................................................................ 35

Solvents and Other Volatile Organic Compounds ............................................................................................. 39

Anthropogenic Factors Related to Occurrence and Distribution................................................................................. 40

Summary and Conclusions .................................................................................................................................................... 46

References Cited.................................................................................................................................................................... 47

Appendixes ............................................................................................................................................................................ 51

1. Summary of ancillary information from respondents to mail-in questionnaire provided to

community water systems participating in the Random Survey ................................................................... 52

2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water

samples collected from May 3, 1999, through October 23, 2000, for the Random Survey,

by type of source water and size of community water system ...................................................................... 66

3. Co-occurrence of volatile organic compounds (VOCs) in source-water samples for the Random

Survey with VOC detections ......................................................................................................................... 80

FIGURES

1. Map showing distribution of drinking-water sources for community water systems in the United States

and Puerto Rico sampled for the Random Survey.................................................................................................... 8

2-6. Graphs showing:

2. Number of source-water samples planned and the number of samples collected per week for

the Random Survey .......................................................................................................................................... 9

3. Percentage of source-water samples planned and the percentage of samples collected per month

for the Random Survey .................................................................................................................................... 10

4. Concentrations of methyl tert-butyl ether (MTBE) in all source-water and field quality-control

samples analyzed for the Random Survey, plotted sequentially by date and time of analysis ........................ 18

5. Concentrations of naphthalene in all source-water and field quality-control samples analyzed

for the Random Survey, plotted sequentially by date and time of analysis ..................................................... 18

6. Comparison of concentrations of m-, p-xylenes in source-water samples and companion field blanks ......... 19

7. Schematic diagram for adjusting the frequency of detection of volatile organic compounds in

source-water samples to reflect possible random sample contamination................................................................. 20
VI Contents

FIGURES—Continued

8-21. Graphs showing:

8. Frequency of detection of volatile organic compounds detected in (A) more than 1.0 percent

of source-water samples and (B) less than 1.0 percent of source-water samples .......................................... 27

9. Cumulative distribution of concentrations of volatile organic compounds detected in

source-water samples from ground-water and surface-water sources............................................................ 28

10. Number of volatile organic compounds detected in source-water samples from ground-water

and surface-water sources .............................................................................................................................. 29

11. Relation between size of community water systems and percentage of drinking-water sources

in urban areas ................................................................................................................................................. 32

12. Frequency of detection of trihalomethanes in source-water samples from ground water,

rivers, and reservoirs ...................................................................................................................................... 33

13. Concentrations of total trihalomethanes in source-water samples from ground water,

rivers, and reservoirs ...................................................................................................................................... 34

14. Frequency of detection of trihalomethanes in ground- and surface-water systems by month ....................... 35

15. Frequency of detection of gasoline compounds in source-water samples from ground water,

rivers, and reservoirs ...................................................................................................................................... 36

16. Concentrations of methyl tert-butyl ether (MTBE) in source-water samples from ground water,

rivers, and reservoirs ...................................................................................................................................... 37

 17. Comparison of concentrations of methyl tert-butyl ether (MTBE) to the sum of the concentrations

of benzene, toluene, ethylbenzene, and xylene (BTEX) in 934 source-water samples ................................. 38

 18. Frequency of detection of methyl tert-butyl ether (MTBE) in source-water samples from

ground-water and surface-water sources by month........................................................................................ 38

 19. Frequency of detection of solvents in source-water samples from ground water, rivers, and reservoirs....... 39

 20. Frequency of detection of refrigerants, fumigants, and organic synthesis compounds in

source-water samples from ground water, rivers, and reservoirs ................................................................... 40

 21. Relation between the frequency of detection of non-trihalomethane volatile organic compounds

and urban land use.......................................................................................................................................... 42

 22. Map showing distribution of methyl tert-butyl ether (MTBE) detections in ground- and surface-water

sources in the United States and Puerto Rico in relation to high MTBE-use areas................................................. 45

TABLES

1. Number of self-supplied community water systems and number of people served, by type

of source water and size of system, November 5, 1998 ......................................................................................... 4

2. Number of community water systems planned and sampled for the Random Survey, by type

of source water and size of system ......................................................................................................................... 5

3. Number of community water systems sampled and planned for the Random Survey, by

source-size category and State................................................................................................................................ 6

4. Volatile organic compounds analyzed for the Random Survey .............................................................................. 12

5. Volatile organic compounds detected in field and trip blanks ................................................................................ 15

6. Number of source-water samples that meet specified conditions with respect to the possibility 

of random contamination........................................................................................................................................ 22

7. Frequency of detection of volatile organic compounds in source-water samples at or above

the minimum reporting level adjusted for random contamination ......................................................................... 23

8. Statistical comparison of the concentrations of volatile organic compounds in 105 companion

field blanks and trip blanks..................................................................................................................................... 24

9. Chemical subgroups of volatile organic compounds detected in source-water samples........................................ 30

10. Statistical comparison of the occurrence of volatile organic compounds in source-water

samples by type of source water............................................................................................................................. 30

11. Statistical comparison of the occurrence of volatile organic compounds in source-water

samples by type of source water and size of community water systems................................................................ 31

12. Statistical comparison of the occurrence of volatile organic compounds in source-water

samples by percentage of urban land use ............................................................................................................... 43
Contents VII

TABLES—Continued

13. Statistical comparison of the occurrence of volatile organic compounds in source-water

samples by population density................................................................................................................................ 43

14. Statistical comparison of the occurrence of methyl tert-butyl ether (MTBE) and other

gasoline-related volatile organic compounds in source-water samples by MTBE-use area .................................. 44

15. Statistical comparison of the occurrence of methyl tert-butyl ether (MTBE) and other

gasoline-related volatile organic compounds in source-water samples by storage-tank density............................ 46

CONVERSION FACTORS AND ABBREVIATIONS

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (° F) as follows:

° F = (1.8 × °C) + 32

Temperature in degrees Fahrenheit (° F) may be converted to degrees Celsius (°C) as follows:

°C = (° F - 32) / 1.8

Concentrations of chemical constituents in water are given in micrograms per liter (μg/L).

Multiply By To obtain

acre 0.4047 hectare

foot (ft) 0.3048 meter

mile (mi) 1.609 kilometer

square mile (mi2) 2.590 square kilometer 

cubic foot per second (ft3/s) 0.02832 cubic meter per second 

million gallons per day (Mgal/d) 0.04381 cubic meter per second
VIII Contents

Other abbreviations used: 

AWWARF, American Water Works Association Research Foundation

BTEX, benzene, toluene, ethylbenzene, and xylenes

CWS, community water system

DIPE, diisopropyl ether

DWCCL, Drinking-Water Candidate Contaminant List

ETBE, ethyl tertiary butyl ether

FRB, field reagent blank

GIS, geographic information system

HA, Health Advisory

km, kilometer

mL, milliliter

MCL, Maximum Contaminant Level

MDL, minimum detection limit

MRL, minimum reporting level

MTBE, methyl tert-butyl ether

MWDSC, Metropolitan Water District of Southern California

NAWQA, National Water-Quality Assessment

NTNCWS, non-transient non-community water system

OHSU, Oregon Health and Science University

OXY, oxygenated gasoline

PWS, public water system

QC, quality control

RFG, reformulated gasoline

SDWIS, Safe Drinking Water Information System

TAME, tert-amyl methyl ether

THM, trihalomethane

TRB, travel reagent blank

TTHM, total trihalomethane

USEPA, U.S. Environmental Protection Agency

USGS, U.S. Geological Survey

VOC, volatile organic compound
Abstract 1

A National Survey of Methyl tert-Butyl Ether and Other 

Volatile Organic Compounds in Drinking-Water 

Sources: Results of the Random Survey

By Stephen J. Grady

ABSTRACT

Methyl tert-butyl ether (MTBE) was 

detected in source water used by 8.7 percent of 

randomly selected community water systems 

(CWSs) in the United States at concentrations that 

ranged from 0.2 to 20 micrograms per liter (μg/L). 

The Random Survey conducted by the U.S. 

Geological Survey, in cooperation with the Metropolitan Water District of Southern California and 

the Oregon Health & Science University, was 

designed to provide an assessment of the frequency of detection, concentration, and distribution of MTBE, three other ether gasoline 

oxygenates, and 62 other volatile organic compounds (VOCs) in ground- and surface-water 

sources used for drinking-water supplies. The 

Random Survey was the first of two components 

of a national assessment of the quality of source 

water supplying CWSs sponsored by the American Water Works Association Research Foundation. A total of 954 CWSs were selected for VOC 

sampling from the population of nearly 47,000 

active, self-supplied CWSs in all 50 States, Native 

American Lands, and Puerto Rico based on a statistical design that stratified on CWS size (population served), type of source water (ground and 

surface water), and geographic distribution 

(State).

At a reporting level of 0.2 μg/L, VOCs were 

detected in 27 percent of source-water samples 

collected from May 3, 1999 through October 23, 

2000. Chloroform (in 13 percent of samples) was 

the most frequently detected of 42 VOCs present 

in the source-water samples, followed by MTBE. 

VOC concentrations were generally less than 

10 μg/L—95 percent of the 530 detections—and 

63 percent were less than 1.0 μg/L. Concentrations 

of 1,1-dichloroethene, tetrachloroethene, trichloroethene, vinyl chloride, and total trihalomethanes 

(TTHMs), however, exceeded drinking-water 

regulations in eight samples.

Detections of most VOCs were more frequent in surface-water sources than in groundwater sources, with gasoline compounds collectively and MTBE individually detected significantly more often in surface water. Use of personal 

and commercial motorized watercraft on surfacewater bodies that are drinking-water sources is 

probably the reason for the elevated detections of 

gasoline contaminants relative to ground water. 

MTBE detections demonstrated a seasonal pattern 

with more frequent detections in surface water in 

summer months, which is consistent with seasonal 

watercraft use.

The detection frequency of most VOCs was 

significantly related to urban land use and population density. Detections of any VOC, non-trihalomethane compounds, gasoline compounds collectively, the specific gasoline compounds benzene, 

toluene, ethylbenzene, and xylenes (BTEX), 

MTBE, solvents, and refrigerants were significantly greater in areas with more than 60 percent 

urban land use and (or) population density greater 

than 1,000 people per square mile than in source 

waters from less urbanized or lower population-
2 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

density areas. MTBE detections were five times 

more frequent in source waters from areas with 

high MTBE use than in source waters from low or 

no MTBE use, but, unlike other gasoline compounds, MTBE detections were not significantly 

related to the density of gasoline storage tanks near 

drinking-water sources. 

INTRODUCTION

The chemical methyl tert-butyl ether (MTBE) 

has been added to gasoline in some areas of the United 

States to control air pollution and to enhance octane 

levels. With the phaseout of tetraethyl lead, MTBE has 

been used nationwide at low concentrations in conventional gasoline since 1979 to enhance octane levels. 

The 1990 Clean Air Act Amendments mandated the 

use of special blends of gasoline that contain oxygenates to reduce summer ozone and winter carbon monoxide levels in nonattainment areas. MTBE is the most 

commonly used gasoline oxygenate in the United 

States. Much of the MTBE used is in reformulated gasoline (RFG) program areas where the concentration of 

MTBE in gasoline is 11-percent by volume and it is 

used year round. When used in oxygenated gasoline 

(OXY) areas, the concentration of MTBE is as much as 

15-percent by volume during the winter months; however, ethanol is the more commonly used oxygenate in 

OXY gasoline.

MTBE may be released into ground water and 

surface water from point sources, such as leaks or 

spills, especially during the distribution, storage, and 

use of the blended gasoline (Zogorski and others, 1997; 

Hitzig and others, 1998; Hunter, 1999; Moran, 

Zogorski, and others, 1999), and nonpoint sources, 

such as automobile and water-craft emissions and evaporative losses, urban precipitation and stormwater 

runoff (Pankow and others, 1997; Baehr and others, 

1999; Moran, Zogorski, and others, 1999). MTBE also 

has been found in spills of home heating oil in Northeastern States, where it may occur as a contaminant in 

the fuel oil as a result of mixing with residual amounts 

of gasoline containing MTBE in the bulk storage, distribution, or delivery of the oil (Robbins and others, 

1999). 

The combination of MTBE’s widespread use and 

frequent release to the environment through leaks and 

spills, together with chemical characteristics such as 

high solubility in water, low soil adsorption, and 

limited biodegradability, has caused extensive contamination of private and public drinking-water supplies. 

Some cities, especially in California, have already lost 

a substantial number of drinking-water sources. In 

Santa Monica, 75 percent of the drinking-water wells 

are unusable due to the presence of MTBE (City of 

Santa Monica, 1999). In South Lake Tahoe, one-third 

of the city’s 34 drinking-water wells have been lost to 

MTBE contamination (Bourelle, 1998). Los Angeles, 

San Francisco, Santa Clara Valley, and Sacramento all 

have wells affected by MTBE (California Department 

of Health Services, 2001). Other cities with affected 

drinking-water supplies include LaCrosse, Kansas 

(Hatten, 2000), and Windham, Maine (State of Maine, 

1998), where officials have taken steps to remediate the 

problem or remove the wells from service. The Interagency Assessment of Oxygenated Fuels (Zogorski 

and others, 1997) concluded that the full extent of 

MTBE occurrence in the Nation’s drinking-water 

supplies could not be described due to limited data and 

recommended that additional data be collected. In 

response to that need, Grady and Casey (2001) assembled finished drinking-water data for a representative 

sample of community water systems (CWSs) in the 

Northeast and Mid-Atlantic regions of the United 

States and reported that MTBE had been found in 

drinking water provided by 106 CWSs that collectively 

serve 2.3 million people. A literature review on MTBE 

in drinking water conducted as part of this assessment 

(Delzer, 2002) found that MTBE has been reported in 

public and (or) private drinking-water supplies in 

36 States. 

The U.S. Environmental Protection Agency 

(USEPA) has tentatively classified MTBE as a possible 

human carcinogen, but no Federal drinking-water standard has been established for MTBE. The USEPA, 

however, has issued a drinking-water advisory that 

MTBE concentrations not exceed 20 to 40 μg/L to avert 

unpleasant taste and odor effects (U.S. Environmental 

Protection Agency, 1997a). The State of California has 

issued a taste and odor limit of 5 μg/L and a Maximum 

Contaminant Level (MCL) of 13 μg/L (California 

Department of Health Services, 2001). The USEPA 

also has required that monitoring for MTBE be conducted by selected CWSs under the Unregulated Contaminant Monitoring Rule (U.S. Environmental 

Protection Agency, 1999a).

Source water is defined by the American Water 

Works Association as “the supply of water for a water 

utility [that] is usually treated before distribution to 
Introduction 3

consumers.” A source water can be a river, brook, 

stream, lake, reservoir, impoundment, spring, or aquifer 

from which a supply of water is obtained. Approximately 180,000 public water systems (PWSs) provide 

drinking water, at least some of the time, to about 252 

million people in the 50 States, the District of 

Columbia, Native American Lands, and Puerto Rico 

(U.S. Environmental Protection Agency, 1997b), and 

about 54,300 of the PWSs are considered CWSs that 

supply water to the same population year round. Solley 

and others (1998) reported that the number of people 

using public-supplied water year round is expected to 

increase; therefore, the potential number of people currently being served by a CWS that contains MTBE in 

the source waters could be substantial and could 

increase in the future.

The U.S. Geological Survey’s (USGS) National 

Water Quality Assessment (NAWQA) Program, in 

cooperation with the Metropolitan Water District of 

Southern California (MWDSC) in LaVerne, California, 

and the Oregon Health & Science University (OHSU) 

in Beaverton, Oregon, conducted a nationwide assessment to determine the occurrence and distribution of 

MTBE and other volatile organic compounds (VOCs) 

in ground waters and surface waters that serve as 

drinking-water supplies. The investigation was sponsored by the American Water Works Association 

Research Foundation (AWWARF). One part of the 

assessment of the extent of MTBE and other VOC 

contamination of source waters was conducted by a 

random survey of CWSs throughout the United States 

that was designed to allow statistical analysis with a 

high degree of confidence in the findings. In addition, 

information about the frequency of detection and concentration of MTBE, other gasoline oxygenates, and 

other VOCs in source water will help accomplish a goal 

of the NAWQA Program—to complete a national 

synthesis of information about VOCs by determining 

the occurrence and distribution of VOCs in ground and 

surface water that serve as drinking-water supplies.

Purpose and Scope

This report presents the findings of the Random 

Survey, the first of two surveys cooperatively conducted by the USGS, MWDSC, and OHSU as part of a 

national assessment of MTBE, other fuel oxygenates, 

and other VOCs in drinking-water sources for CWSs, 

that was sponsored by the AWWARF. The Random 

Survey was designed to provide representative 

information on the occurrence (frequency of detection 

and concentration) and distribution of MTBE, three 

other gasoline oxygenates, and 62 other VOCs in 

untreated, ground- and surface-water sources of 

drinking water used by CWSs in the United States. 

The statistical design of the Random Survey also was 

intended to allow hypothesis testing of factors that 

may be related to more frequent detection of MTBE 

and other VOCs in drinking-water sources. 

Information was collected on the quality of 

water from 954 drinking-water sources in all 50 

States, Native American lands, and Puerto Rico for the 

Random Survey. The source-water samples were collected by participating CWSs from May 3, 1999 to 

October 23, 2000. This report describes the results of 

the chemical analyses of the source-water samples and 

also presents results of statistical analysis used to 

identify differences in the occurrence and distribution 

of MTBE and other VOCs that relate to the type of 

source water, size of systems, and other characteristics 

of the CWS drinking-water sources sampled for this 

study.

Acknowledgments

This study and assessment would not have been 

possible without the cooperation and assistance of the 

owners, operators, and staff of the 954 water systems 

that provided information on the characteristics of 

their water sources and the operation of their water 

system, and who conscientiously collected and submitted the necessary water samples. All chemical 

analyses for VOCs in source-water samples were 

conducted at the MWDSC laboratory in LaVerne, 

California, under the direction of Bart Koch and 

Melissa Dale. The author would like to thank George 

D. Casey, Rick Clawges, Tammy Ivahnenko, and 

Erika Schoen of the USGS for their efforts in compiling and analyzing the electronic data provided by 

the USEPA, the participating CWSs, the MWDSC, 

and other sources that was fundamental to the successful completion of the Random Survey. Finally, the 

author also would like to thank Bart Koch of the 

MWDSC, Paul Tratnyek of OHSU, John Zogorski and 

Gregory Delzer of the USGS, and members of the 

AWWARF project advisory committee for their technical questions, comments, and suggestions during the 

design and implementation of this study, and Lori 

Apodaca and Gregory Delzer of the USGS for their 

technical review of this report.
4 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

IMPLEMENTATION OF THE RANDOM SURVEY

The Random Survey was designed to ensure an 

unbiased distribution of CWSs by State, type of source 

water (ground water or surface water), and population 

served (Ivahnenko and others, 2001). A statistical sampling of a subset of CWSs would allow information on 

the frequency of occurrence and concentration of 

MTBE and other VOCs in drinking-water sources for 

randomly selected CWSs to represent, in aggregate, the 

overall population of CWSs.

Data on the distribution of the nearly 47,000 

active, self-supplied CWSs that serve more than 250 

million people (table 1) were obtained from the 

USEPA’s Safe Drinking Water Information System 

(SDWIS) on November 5, 1998 (U.S. Environmental 

Protection Agency, 1998b). By design, the Random 

Survey would distribute 1,000 samples among 10 

source-size categories (5 for ground water, 5 for surface water) stratified to reflect the national distribution 

of the self-supplied systems and the total number of 

people served by CWSs within each category (Ivahnenko and others, 2001). Because more than 60 percent 

of CWSs are very small (serve 25 to 500 people) and 

are supplied by ground-water sources, but 45 percent 

of the population served by CWSs are customers of 

very large (more than 50,000 people served), surfacewater supplied systems, population density and sourcewater type were weighted equally in the design of the 

Random Survey. Consequently, the distribution of the 

1,000 CWSs planned for the Random Survey included 

613 mostly very small and small, ground-watersupplied systems and 387 predominantly large and 

very large, surface-water-supplied systems. 

The Random Survey was conducted over a 78-

week period that began on May 3, 1999 and ended on 

October 23, 2000. Selection of participating CWSs was 

made from randomized lists of the 46,960 active, selfsupplied water utilities obtained from the SDWIS database on November 5, 1998, until the requisite number 

of systems was obtained for each source-size category 

in each State, Native American Lands, and Puerto 

Rico. Subsequently, sample-collection kits were distributed to the selected CWSs.

A total of 954 source-water samples were submitted to the MWDSC laboratory by the CWSs randomly selected for participation in the survey. With 

participation by 95 percent of the CWSs included in the 

design, the sample size achieved was sufficiently close 

to the total 1,000 planned systems for the Random 

Survey to accomplish the designed distribution and to 

allow valid statistical analysis.

The distribution of the 954 participating CWSs 

by source-water type and system size is shown in 

table 2. The percentage of ground-water sources sampled for each of the five size categories ranged from 92 

to 100 percent of the number planned in the design, and 

the percentage of the surface-water sources sampled 

ranged from 86 to 99 percent of the number planned.

 Table 1. Number of self-supplied community water systems and number of people served, by type of source water 

and size of system, November 5, 1998

[Data from U.S. Environmental Protection Agency’s Safe Drinking Water Information System (URL http://www.epa.gov/enviro/html/sdwis/). 

CWS, community water system. CWS size categories: very small, serving less than 500 people; small, serving 501 to 3,300 people; medium, 

serving 3,301 to 10,000 people; large, serving 10,001 to 50,000 people; very large, serving more than 50,000 people]

CWS size

 category

Ground water Surface water

Number

 of 

systems

Percent 

of all 

systems

Number of

people served

Percent 

of total 

population 

served

Number of 

systems

Percent 

of all 

systems

Number of

people served

Percent 

of total 

population 

served

Very small 28,324 60.3 4,625,130 1.84 1,228 2.64 616,012 0.24

Small 9,775 20.8 14,178,037 5.63 1,562 3.33 5,739,217 2.28

Medium 2,399 5.11 14,219,831 5.65 971 2.07 11,045,463 4.39

Large 1,194 2.54 25,342,137 10.1 928 1.98 36,525,585 14.5

Very large 182 .39 25,696,338 10.2 397 .85 113,671,630 45.2

Total 41,874 89.1 84,061,473 33.4 5,086 10.9 167,597,907 66.6
Implementation of the Random Survey 5

Table 2. Number of community water systems planned and sampled for the Random Survey, by type of source water 

and size of system

[CWS, community water system; CWS size categories: very small, serving fewer than 500 people; small, serving 501 to 3,300 people; medium, 

serving 3,301 to 10,000 people; large, serving 10,001 to 50,000 people; very large, serving more than 50,000 people]

CWS size 

category

Type of source water and 

number of systems planned 

Type of source water and 

number of systems sampled

Type of source water and 

percent of planned

systems sampled

Ground

 water

Surface

 water Total Ground  water

Surface

 water Total Ground water

Surface 

 water Total

Very small 311 14 325 292 12 304 94 86 94

Small 132 28 160 121 26 147 92 93 92

Medium 54 32 86 50 30 80 93 94 93

Large 63 83 146 63 79 142 100 95 97

Very large 53 230 283 53 228 281 100 99 99

Total 613 387 1,000 579 375 954 94 97 95

Geographic Distribution of Participating 

Community Water Systems

 The geographic distribution of systems sampled 

is within 90 percent of the target proportion for 45 of 

the 52 States or other geographic entities (table 3). The 

only substantial difference in the achieved distribution 

of CWSs from the design was the selection of only 

14 of 22 planned systems in U.S. Territories, and that 

all 14 of these are in Puerto Rico. The logistical difficulties of locating and contacting potential participating CWSs in other U.S. Territories required this 

modification in design. Overall, the achieved distribution has a slight deficit in the number of smaller systems for both surface- and ground-water-supplied 

CWSs. Generally, it was considerably more difficult to 

obtain participants from the smallest size categories, 

and the total population of very small surface-water 

supplied systems is limited. For some States, failure by 

the one or two systems in these categories to participate 

in the survey provided no alternative selections.

The percentage of planned systems sampled in 

each State ranged from 67 to 100 percent for groundwater supplied systems and from 59 to 100 percent for 

surface-water supplied systems. A small deficit in participating ground-water systems occurred in almost 

half the States, mostly for the very small and small 

systems. The very small systems typically have parttime operators and management, and often there were 

difficulties in making contact with or obtaining the 

samples from very small ground-water supplied systems. 

The geographic distribution of the 579 groundwater sources and 375 surface-water sources in the 

50 States, Native American lands, and Puerto Rico 

sampled for the Random Survey are shown in figure 1. 

Nearly all (98 percent) of the ground-water sources 

were wells (2 percent were springs). Surface-water 

sources included 204 lakes and (or) reservoirs 

(54 percent), and 171 rivers, streams, aqueducts, or 

canals (46 percent). Fifty-five percent of the drinkingwater sources sampled in the Random Survey are east 

of the Mississippi River. Proportionally, more CWSs in 

the east have surface-water sources than those in the 

west, where ground-water sources make up two-thirds 

of source waters sampled. The distribution of source 

waters also reflects regional physiographic and hydrogeologic characteristics. Ground-water sources are 

predominant in much of the southeastern Atlantic and 

Gulf of Mexico coastal plain in Georgia, Florida, 

Mississippi, and Louisiana, and in the High Plains that 

are underlain by productive aquifers. Surface-water 

sources are more dominant in the humid Appalachian 

and Ozark Mountain areas and along the shores of the 

Great Lakes.
6 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Table 3. Number of community water systems sampled and planned for the Random Survey, by source-size category 

and State

[GW, ground water; SW, surface water; VSM, very small; SM, small; MED, medium; LRG, large; VLRG, very large]

State or other 

entity

Number of CWSs sampled/number of CWSs planned

Percentage

of 

planned

Source-size category

GW- Total

VSM

GWSMGWMEDGWLRGGWVLRGSWVSMSWSMSWMEDSWLRGSWVLRG

AK 4/4 1/1 0 0 0 1/1 0 0 0 1/1 7/7 100

AL 0/0 2/2 2/2 1/1 0 0 0 1/1 3/3 5/5 14/14 100

AR 2/2 2/2 1/1 0 0 0 0/1 1/1 1/1 1/1 8/9 89

AZ 5/5 2/2 1/1 2/2 1/1 0 0 0 0 6/6 17/17 100

CA 19/20 5/5 4/3 7/7 11/11 2/2 2/2 2/2 5/5 30/30 87/87 100

CO 4/5 1/1 0 0 0 1/1 1/1 0/1 2/2 6/6 15/17 88

CT 5/5 1/1 0 0 0 0 0 0 2/2 5/5 13/13 100

DE 2/2 1/1 0 0 0 0 0 0 0 1/1 4/4 100

FL 13/13 5/6 3/3 7/7 17/17 0 0 0 1/1 3/3 49/50 98

GA 11/12 2/3 1/1 1/1 1/1 0 1/1 1/1 3/3 8/8 29/31 94

HI 0 1/1 0 0 1/1 0 0 0 0 0 2/2 100

IA 7/7 4/4 1/1 1/1 1/1 0 0 0 0 2/2 16/16 100

ID 5/5 1/1 1/1 1/1 0 1/1 0 0 0 1/1 10/10 100

IL 7/7 4/5 2/2 2/2 1/1 0 1/1 1/1 3/3 8/8 29/30 97

IN 4/4 4/4 2/2 2/2 1/1 0 0 1/1 1/1 4/4 19/19 100

KS 4/4 3/3 0 1/1 0 0 1/1 1/1 1/1 3/3 14/14 100

KY 1/1 0 0 0 0 0 1/1 2/2 4/5 2/2 10/11 91

LA 8/8 5/5 1/3 2/2 1/2 0 0 1/1 1/1 5/5 24/27 89

MA 2/2 0/1 2/2 3/3 1/1 0 0 1/1 4/4 8/8 21/22 95

MD 3/4 1/1 1/1 1/1 0 0 0 0 1/1 5/5 12/13 92

ME 2/2 1/1 0 0 0 0 1/1 0 1/1 0 5/5 100

MI 8/9 4/4 1/1 1/1 1/1 0 0 1/1 2/2 4/4 22/23 96

MN 5/6 4/4 1/1 3/3 0 0 0 0 1/1 2/2 16/17 94

MO 8/8 4/4 2/2 1/1 1/1 0 1/1 1/1 1/1 4/4 23/23 100

MS 5/5 8/9 3/3 2/2 0 0 0 0 0 0 18/19 95

MT 4/5 1/1 0 0 0 0 0 0 0 1/1 6/7 86

NC 15/16 3/3 1/1 1/1 0 0 1/1 2/2 4/4 7/7 34/35 97

ND 1/1 1/1 0 0 0 0 0 0 1/1 0 3/3 100

NE 5/5 2/2 1/1 1/1 0 0 0 0 0 1/1 10/10 100

NH 5/5 1/1 0 0 0 0 0 0 1/1 1/1 8/8 100

NJ 3/3 2/2 2/2 4/4 1/1 0 0 0 1/1 8/8 21/21 100

NM 5/5 1/1 1/1 1/1 1/1 0 0 0 0 0 9/9 100

NV 2/2 1/1 0 0 0 0 0 0 0 1/1 4/4 100

NY 12/15 3/4 1/1 3/3 4/4 1/1 2/2 2/2 4/4 16/16 48/52 92

OH 7/7 4/4 2/2 3/3 2/2 0 1/1 1/1 4/4 10/10 34/34 100
Implementation of the Random Survey 7

OK 3/3 1/2 1/1 1/1 0 1/1 2/2 2/2 2/2 4/4 17/18 94

OR 5/6 1/1 0 1/1 0 1/1 1/1 1/1 2/2 2/2 14/15 93

PA 11/14 4/5 2/2 1/1 0 1/1 1/1 2/2 6/6 15/15 43/47 92

RI 0 0 0 0 0 0 0 0 0 1/1 1/1 100

SC 3/4 1/1 1/1 0 0 0 0 0 2/2 3/3 10/11 91

SD 2/2 1/1 0 0 0 0 0 0 0 1/1 4/4 100

TN 1/1 1/1 1/1 1/1 1/1 0 1/1 2/2 4/4 4/4 16/16 100

TX 25/24 12/14 3/6 3/3 3/3 0/1 1/2 2/2 5/5 17/17 71/77 92

UT 3/3 1/1 1/1 1/1 0 0 0 0 0 4/4 10/10 100

VA 11/11 2/2 0 0 0 0 1/1 1/1 2/2 6/6 23/23 100

VT 2/3 1/1 0 0 0 0 1/1 0 0 0 4/5 80

WA 15/17 4/4 1/1 2/2 1/1 1/1 1/1 0 1/1 2/2 28/30 93

WI 7/7 4/4 2/2 1/1 1/1 0 0 0 1/1 3/3 19/19 100

WV 2/2 0/1 0 0 0 0 2/2 1/1 1/1 1/1 7/8 88

WY 2/2 0 0 0 0 0 0 0 0 0 2/2 100

NA1 6/6 2/2 0 0 0 1/1 0 0 0 0 9/9 100

PR2 1/2 1/1 1/1 1/1 0 1/2 2/2 0/1 1/4 6/8 14/22 64

Total 292/

311

121/

132

50/

54

63/

63

53/

53

12/

14

26/

28

30/

32

79/

83

228/

230

954/ 

1,000

95

Percentage of 

planned

94 92 93 100 100 86 93 94 95 99 95

1

Native Americans Lands.

2

Puerto Rico.

Table 3. Number of community water systems sampled and planned for the Random Survey, by source-size category 

and State–Continued

[GW, ground water; SW, surface water; VSM, very small; SM, small; MED, medium; LRG, large; VLRG, very large]

State or other 

entity

Number of CWSs sampled / number of CWSs planned

Percentage

of 

planned

Source-size category

GW- Total

VSM

GWSMGWMEDGWLRGGWVLRGSWVSMSWSMSWMEDSWLRGSWVLRG
8 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Figure 1. Distribution of drinking-water sources for community water systems in the United States and Puerto Rico sampled for the Random 

GROUND-WATER SOURCESURFACE-WATER SOURCE

Survey.

EXPLANATION
Implementation of the Random Survey 9

Temporal Distribution of Source-Water 

Samples

Sample collection for the Random Survey was 

designed to provide an even distribution of the number 

of samples collected in any particular month or season. 

The temporal distribution of the 1,000 source-water 

samples planned for in the design of the Random 

Survey was to spread the sample collection over a 64-

week period in such a way as to preclude seasonal bias 

in the data (Ivahnenko and others, 2001). To achieve an 

equal number of samples on a monthly basis for a 

calendar year, about 83 samples (or 8 percent of the 

samples) should be collected each month. Because the 

sampling was planned to extend beyond a calendar 

year, only about one-half as many samples would be 

collected each week during the initial and final 

12 weeks of the survey (collectively) as were scheduled 

during the intervening 40 weeks (fig. 2). The actual 

sampling period, however, extended for 78 weeks 

(from May 3, 1999 through October 23, 2000) 

as logistical considerations (such as holiday work 

schedules) and the need to reselect and (or) reschedule 

some participating CWSs caused deviation from the 

designed sample frequency. Because of the difficulties 

experienced in locating the requisite number of small 

CWSs to participate in the Random Survey, the sample 

period (fig. 2) was extended to allow for participation 

by as many CWSs as could be arranged. The modifications in the sampling schedule did skew the temporal 

pattern of the samples from the even distribution 

planned. The percentage of all samples collected 

during any particular month of the year exceeded the 

planned 8 percent per month during the summer 

months (fig. 3). In particular, the number of samples 

submitted during August was almost 150 percent of the 

target, whereas a deficit occurred during the fall and 

early winter months, especially November and 

December. The geographic distribution of drinkingwater sources sampled in any month was random, however, and it is considered unlikely that the occurrence of 

MTBE or other VOCs determined during the Random 

Survey was affected by the temporal variations in 

sample allocation.

Figure 2. Number of source-water samples planned and the number of samples collected per week for the Random 

Survey.

0

5

10

15

20

25

30

1 6 11 16 21 26 31 36 41 46 51 56 61 66 71 76

WEEK NUMBER

NUMBER OF SAMPLES

Planned

Collected
10 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

DATA COLLECTION AND ANALYSIS

The findings of the Random Survey are based on 

information obtained and reviewed as part of four data 

collection and analysis activities described in the 

following sections of the report: (1) collection and laboratory chemical analysis of source-water and companion field, quality-control samples, (2) application of 

appropriate data analysis and interpretation methods, 

(3) review of the quality-control data to assure that 

data-quality objectives were met, and (4) collection and 

compilation of ancillary information on the drinkingwater sources and other geospatial data that may 

contribute to a better understanding of the occurrence 

and distribution of MTBE and other VOCs in source 

water. While the overall design for this assessment has 

been previously documented (Ivahnenko and others, 

2001) and is not be repeated here, additional information on the data collection, review, documentation, 

and analysis are described below for the reader’s 

convenience.

Collection of Source-Water and QualityControl Samples

All source-water samples for the Random Survey 

were collected by CWS personnel. Sample kits with 

baked-glass vials, VOC-free reagent water for field 

blanks, and instructions for collecting the VOC samples 

were provided by MWDSC to CWS personnel, with 

emphasis on collecting a raw (untreated) source-water 

sample. Two drops of 50-percent dilute hydrochloric 

acid were added to 40-mL (milliliter) baked-glass vials 

prior to shipment to the CWS. Samples for the Random 

Survey were analyzed for MTBE, three other gasoline 

oxygenates—ethyl tert-butyl ether (ETBE), diisopropyl ether (DIPE), and tert-amyl methyl ether 

(TAME)—plus 62 additional VOCs (table 4) at the 

MWDSC laboratory using the USEPA-approved 

method 524.2 (U.S. Environmental Protection Agency, 

1995).

Most source-water samples submitted to the 

MWDSC laboratory were accompanied by one or more 

Figure 3. Percentage of source-water samples planned and the percentage of samples collected per month for the

Random Survey.

0

2

4

6

8

10

12

14

JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC

MONTH

PERCENT OF SAMPLES

Planned

Collected
Data Collection and Analysis 11

reagent-water blanks. Commercially produced, VOCfree reagent water was routinely tested at the MWDSC 

laboratory to ensure purity and sent to the CWSs to be 

used for collecting field reagent blanks (FRBs). Instructions were given to fill the empty glass vials labeled 

“Field Blank” at each sample site with the VOC-free 

water provided in the sample kit, at the same time the 

source-water sample was collected. FRBs were collected and processed in the same location as the sourcewater sample, thereby exposing the blank water to 

sampling conditions. FRBs also were preserved with 

one or two drops of 50-percent dilute hydrochloric acid, 

but in general, were analyzed only if VOCs were 

detected in the corresponding environmental sample. 

Travel reagent blanks (TRBs) also accompanied most 

environmental samples. TRB vials were prepared at the 

MWDSC laboratory by filling 40-mL baked-glass vials 

with VOC-free water. TRBs were never uncapped by 

the samplers, and like the FRBs, were generally analyzed only if VOCs were detected in the environmental 

sample.

A total of 956 source-water samples and 402 

quality-control (QC) samples were submitted to the 

MWDSC laboratory in LaVerne, California during the 

78-week sample-collection period. Except for two 

CWSs, samples were collected only once by each of 

954 CWSs that participated in the survey. The extra two 

samples were kept in the database for a data-quality 

review, but they were not included in the data analysis 

for occurrence and distribution of VOCs. 

Analysis of Data

Statistical summaries of the data, presented in 

tabular and graphical formats in this report, are used to 

describe the occurrence and distribution of MTBE and 

VOCs in drinking-water sources. Descriptive statistics 

include number of samples, number of detections, the 

frequency of detection (percentage of samples with 

detections), detectable concentration range, and 

medians of detected VOC concentrations. Because the 

data for all VOCs reported by the MWDSC laboratory 

are highly censored, that is, 50 percent or more (and 

commonly 90 percent or more) of concentrations are 

below the minimum reporting level (MRL), median 

concentrations or other statistical measures of central 

tendency (mean) or spread (standard deviation, interquartile range, or most other percentiles of the samplepopulation distribution) cannot be determined. Medians 

of the concentrations above the MRL, although a 

positively biased indication of the median VOC 

concentration for sample populations, are provided 

because this statistic affords the only comparison of 

concentrations among such highly censored analytes. 

Descriptive and nonparametric statistics, histograms, cumulative frequency plots, and scatter plots 

(Helsel and Hirsch, 1992) are used in this report to 

describe the frequency of detection and concentration 

of MTBE and other VOCs in drinking-water sources. 

The data are summarized to show the occurrence and 

distribution in relation to the type of source water 

(ground water, surface water, reservoirs and rivers) 

and to the size of the CWSs (five categories based on 

population served). Maps show the location of 

drinking-water sources (wells, springs, and surfacewater intakes) where samples were collected for 

analyses of MTBE and selected other VOCs, and the 

location of drinking-water sources where these compounds were detected. Where appropriate, a variety of 

hypothesis tests including contingency-table tests 

(Pearson’s chi-square test with Yates’ continuity correction), Kruskal-Wallis tests, and the Wilcoxon 

signed rank test (Iman and Conover, 1983; Helsel and 

Hirsch, 1992), were used to test for relations between 

the frequency of detection or concentrations of VOCs 

and anthropogenic factors such as land use, population 

density, and the distribution of high MTBE-use areas.

Contingency-table tests are used in this report 

because the highly censored VOC analytical data 

largely precludes analysis by hypothesis tests that 

evaluate continuous variables. Contingency tables 

measure the association between two discrete, categorical variables. For example, is the probability of 

detecting a VOC (compared to the probability of nondetection) related to a type of source water, the size of 

CWSs, land use, or the presence or absence of some 

other anthropogenic factor? The data are arranged into 

a matrix of rows and columns—with no natural 

ordering—and the distribution of data among the categories is tested to determine if the row classification 

is independent of the column using the chi-square distribution (Helsel and Hirsch, 1992). As with other 

statistical tests used in this report, the results of the 

contingency-table tests are expressed by the “p-value” 

or the significance level attained by the data; for this 

report, the null hypothesis is rejected and the two variables are determined to be significantly related at 

p-values less than 0.05 (95-percent confidence level). 

When the variables are found to be dependent or 

related, however, it is not necessarily implied that one 

variable causes the observed response in the second 

variable.
12 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Table 4. Volatile organic compounds analyzed for the Random Survey

[MDL, method detection limit; MRL, minimum reporting level; USEPA, U.S. Environmental Protection Agency; MCL, USEPA

Maximum Contaminant Level; HA, USEPA Health Advisory; DWCCL, USEPA Drinking-Water Contaminant Candidate List;

μg/L, microgram per liter; --, not applicable]

Volatile organic compound 

(abbreviation)

MDL

(μg/L)

MRL

(μg/L)

 MCL1

(μg/L)

HA1

(μg/L) DWCCL2

Gasoline Oxygenates

Ethyl tert-butyl ether (ETBE) 0.034 0.2 -- -- --

Diisopropyl ether (DIPE) .073 .2 -- -- --

tert-Amyl methyl ether (TAME) .025 .2 -- -- --

Methyl tert-butyl ether (MTBE) .039 .2 -- 20-40 Yes

Other Gasoline Compounds

Benzene .029 .2 5 -- --

n-Butylbenzene .047 .2 -- -- --

sec-Butylbenzene .044 .2 -- -- --

tert-Butylbenzene .037 .2 -- -- --

Ethylbenzene .033 .2 700 700 --

Naphthalene .055 .2 -- 100 Yes

Toluene .025 .2 1,000 1,000 --

1,3,5-Trimethylbenzene .026 .2 -- -- --

m-, p-Xylene .065 .2 10,000 10,000 --

o-Xylene .028 .2 10,000 10,000 --

Trihalomethane Disinfectant By-Products

Bromodichloromethane .018 .2 (

3

) -- --

Bromoform .022 .2 (

3

) -- --

Chloroform .024 .2 (

3

) -- --

Chlorodibromomethane .016 .2 (

3

) 60 --

Solvents

Bromobenzene .029 .2 -- -- Yes

Methyl ethyl ketone .645 2.0 -- -- --

Carbon tetrachloride .049 .2 5 -- --

Chlorobenzene .032 .2 100 100 --

Chloroethane .095 .2 -- -- --

2-Chlorotoluene .033 .2 -- 100 --

4-Chlorotoluene .030 .2 -- 100 --

Dibromomethane .028 .2 -- -- --

1,2-Dichlorobenzene .037 .2 600 600 --

1,3-Dichlorobenzene .029 .2 -- 600 --

1,1-Dichloroethane .036 .2 -- -- Yes

1,2-Dichloroethane .029 .2 5 -- --

1,1-Dichloroethene .082 .2 7 7 --

cis-1,2-Dichloroethene .024 .2 70 70 --

trans-1,2-Dichloroethene .040 .2 100 100 --

1,2-Dichloropropane .028 .2 5 -- --

1,1,1,2,2,2-Hexachloroethane .086 .2 -- 1 --

Methylene chloride .021 .2 5 -- --

n-Propylbenzene .043 .2 -- -- --
Data Collection and Analysis 13

1

U.S. Environmental Protection Agency, 2000.

2

U.S. Environmental Protection Agency, 1998a.

3Maximum Contaminant Level for total trihalomethanes is 80 μg/L.

Solvents—Continued

1,1,1,2-Tetrachloroethane 0.020 0.2 -- 70 --

1,1,2,2-Tetrachloroethane .026 .2 -- -- Yes

Tetrachloroethene (PCE) .049 .2 5 -- --

1,2,4-Trichlorobenzene .042 .2 70 70 --

1,1,1-Trichloroethane .045 .2 200 200 --

1,1,2-Trichloroethane .014 .2 5 3 --

Trichloroethene (TCE) .034 .2 5 -- --

1,2,3-Trichloropropane .027 .2 -- 40 --

Fumigants

Bromomethane .084 .2 -- 10 Yes

1,4-Dichlorobenzene .033 .2 75 75 --

cis-1,3-Dichloropropene .024 .2 -- -- Yes

trans-1,3-Dichloropropene .026 .2 -- -- Yes

Refrigerants

Chloromethane .105 .2 -- 3 --

Dichlorodifluoromethane .121 .2 -- 1,000 --

Trichlorofluoromethane .096 .2 -- 2,000 --

1,1,2-Trichloro-1,2,2-trifluoroethane .099 .2 -- -- --

Organic Synthesis Compounds

Acrylonitrile .098 .2 -- -- --

Bromochloromethane .036 .2 -- 90 --

1,3-Dichloropropane .029 .2 -- -- Yes

2,2-Dichloropropane .056 .2 -- -- Yes

1,1-Dichloropropene .060 .2 -- -- Yes

Hexachlorobutadiene .057 .2 -- 1 Yes

Isopropylbenzene .040 .2 -- -- --

p-Isopropyltoluene .037 .2 -- -- Yes

Styrene .026 .2 100 100 --

1,2,3-Trichlorobenzene .042 .2 -- -- --

1,2,4-Trimethylbenzene .022 .2 -- -- Yes

Vinyl bromide .084 .2 -- -- --

Vinyl chloride .082 .2 2 -- --

Table 4. Volatile organic compounds analyzed for the Random Survey–Continued

[MDL, method detection limit; MRL, minimum reporting level; USEPA, U.S. Environmental Protection Agency; MCL, USEPA

Maximum Contaminant Level; HA, USEPA Health Advisory; DWCCL, USEPA Drinking-Water Contaminant Candidate List;

μg/L, microgram per liter; --, not applicable]

Volatile organic compound 

(abbreviation)

MDL

(μg/L)

MRL

(μg/L)

 MCL1

(μg/L)

HA1

(μg/L) DWCCL2
14 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Review of Field Quality-Control Data

The field quality-control (QC) data collected in 

conjunction with the Random Survey were reviewed 

and the results are presented here. Field reagent (FRB) 

and trip reagent (TRB) blanks were used to measure 

any systematic or random contamination from the environment around the sample site and during the sample 

shipment. In addition to data for 956 source-water samples, the MWDSC laboratory reported VOC analyses 

for 290 FRBs and 112 TRBs. Although field blank vials 

and VOC-free reagent water were provided to all 

CWSs, not all FRBs were received or analyzed. A small 

number (21) of CWSs omitted processing and returning 

the field blank with their sample vials (or their FRBs 

were broken in transit), and the FRBs and TRBs generally were not analyzed unless VOCs were detected in 

the companion source-water samples. TRBs were not 

included in the sample kits provided to the CWSs until 

week 16 of the Random Survey.

The QC data indicate that some samples may 

have been contaminated because 93 percent of the 

FRBs and 92 percent of the TRBs analyzed contained 

one or more VOCs at concentrations equal to or greater 

than the method detection limit (MDL). Forty-three of 

the 56 VOCs detected in source-water samples were 

reported in 1 or more of the 290 FRBs at concentrations 

equal to or greater than the MDL, and 20 of these compounds were detected in 1 or more of the 112 TRBs 

(table 5). Toluene and methylene chloride were the 

most frequently detected VOCs, reported at concentrations equal to or above their MDLs in nearly threequarters of the FRB and TRBs, but nine additional 

VOCs, including MTBE, were reported in more than 10 

percent of the FRBs and TRBs (table 5). The contamination was largely low-level, however, and most (80 

percent) VOC concentrations in the field and trip 

blanks were less than the MRL (equal to 0.2 μg/L for 

all VOCs except for methyl ethyl ketone, which has an 

MRL of 2.0 μg/L). Still, 25 of the VOCs detected in 

FRBs and 8 of the VOCs detected in TRBs were 

measured in some QC samples at concentrations equal 

to or above the MRL.

The extensive low-level contamination evident in 

the field QC data prevented reporting the occurrence of 

VOCs in source water at concentrations below the 

MRL; however, because contamination was measured 

in 108 FRBs (37 percent) and 10 TRBs (8.9 percent) at 

concentrations at or above the MRL, the field QC data 

were analyzed further to determine the level of uncertainty associated with VOC detection frequencies in 

source water reported at the MRL. The procedures used 

to evaluate and quantify the extent of external sample 

contamination and the implications for the sourcewater findings are described below.

The additional analysis of field QC data included 

the following steps. First, the concentrations of VOCs 

in all source-water and QC-samples were plotted in 

relation to the sequence in time when each sample was 

analyzed by the MWDSC laboratory. Such plots can 

demonstrate the occurrence of temporal anomalies in 

VOC detections that may represent a systematic bias or 

periodic contamination that may be related to field and 

(or) laboratory methods and performance. The results 

of all source-water and field-QC sample analyses for 

MTBE and naphthalene, respectively, ordered sequentially by date and time of analysis during the 78-week 

duration of the Random Survey, are shown in figures 4 

and 5. The plots show that although detections of 

MTBE were measured throughout the period without 

any apparent bias associated with any particular time 

increment, the naphthalene detections were more frequent at certain times during the analytical time span. 

Periods when naphthalene detections were disproportional may correspond to some phenomenon in the laboratory analytical procedure or environment that 

produced systematic naphthalene contamination of the 

samples during those periods. Low-level detects 

(<MRL) of high molecular weight analytes such as 

naphthalene have been observed to occur after the analysis of a spiked sample and have been attributed to 

“carry over” of the analyte on the sorbent purge trap 

(B. Koch, Metropolitan Water District of Southern 

California, written commun., 2002). Nearly all the 

naphthalene concentrations were below the MRL of 

0.2 μg/L, however, and consequently, any apparent systematic naphthalene contamination would be nullified 

by conducting the data analysis at that level. Three 

other analytes—1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, and p-isopropyltoluene—demonstrated 

similar temporal patterns of clustered detections within 

specific time periods of the analytical time span, but all 

detections of the three compounds were below their 

MRLs and, consequently, are not problematic for interpretations of the source-water data at the MRL.
Data Collection and Analysis 15

Table 5. Volatile organic compounds detected in field and trip blanks

[MDL, method detection limit; MRL, minimum reporting level, μg/L, microgram per liter]

Volatile organic 

compound

Blank Number of 

detections Range of 

concentration 

(μg/L)

Frequency of detection

(percent)

Type Number

At or

 above

 MDL

At or

 above

 MRL

At or above 

the MDL

At or above 

the MRL

Benzene field 290 44 2 0.03 - 0.23 15 0.7

Benzene trip 112 2 0 .03 - .06 1.8 0

Bromobenzene field 290 1 0 .05 .3 0

Bromobenzene trip 112 1 0 .04 .9 0

Bromochloromethane field 290 1 0 .06 .3 0

Bromochloromethane trip 112 0 0 not detected 0 0

Bromodichloromethane field 290 9 1 .02 - 5.3 3.1 .3

Bromodichloromethane trip 112 0 0 not detected 0 0

Bromoform field 290 2 2 .02 - 1.2 .7 .7

Bromoform trip 112 0 0 not detected 0 0

Bromomethane field 290 1 0 .11 .3 0

Bromomethane trip 112 0 0 not detected 0 0

Chlorodibromomethane field 290 4 1 .03 - 1.6 1.4 .3

Chlorodibromomethane trip 112 0 0 not detected 0 0

Chloroform field 290 61 5 .03 - 12. 21 1.7

Chloroform trip 112 17 0 .03- .07 15 0

Chloromethane field 290 2 2 .60 - 1.2 .7 .7

Chloromethane trip 112 0 0 not detected 0 0

2-Chlorotoluene field 290 1 0 .05 0.3 0

2-Chlorotoluene trip 112 0 0 not detected 0 0

1,4-Dichlorobenzene field 290 8 3 .04 - 3.7 2.8 1.0

1,4-Dichlorobenzene trip 112 1 0 .08 0 0

1,1-Dichloroethane field 290 1 0 .12 .3 0

1,1-Dichloroethane trip 112 0 0 not detected 0 0

1,1-Dichloroethene field 290 1 0 .09 0.3 0

1,1-Dichloroethene trip 112 0 0 not detected 0 0

cis-1,2-Dichloroethene field 290 1 0 .15 .3 0

cis-1,2-Dichloroethene trip 112 0 0 not detected 0 0

Dibromomethane field 278 1 0 .07 .4 0

Dibromomethane trip 112 0 0 not detected 0 0

Dichlorodifluoromethane field 290 3 2 .13 - .21 1.0 .7

Dichlorodifluoromethane trip 112 0 0 not detected 0 0
16 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

1,2-Dichloropropane field 278 1 0 0.09 0.4 0

1,2-Dichloropropane trip 112 0 0 not detected 0 0

1,3-Dichloropropane field 282 3 0 .03 - .09 1.1 0

1,3-Dichloropropane trip 112 1 0 .03 .9 0

Ethylbenzene field 290 104 34 .04 - 1.6 36 12

Ethylbenzene trip 112 9 1 .04 - 1.1 8.0 .9

Ethyl tert-butyl ether field 290 2 0 .16 - .19 .7 0

Ethyl tert-butyl ether trip 112 0 0 not detected 0 0

Isopropylbenzene field 290 31 11 .04 - .53 11 3.8

Isopropylbenzene trip 112 2 1 .04 - .27 1.8 .9

p-Isopropyltoluene field 290 3 0 .04 - .05 1.0 0

p-Isopropyltoluene trip 112 1 0 .05 .9 0

Methyl ethyl ketone field 290 15 4 .81 - 4.0 5.5 1.4

Methyl ethyl ketone trip 112 0 0 not detected 0 0

Methyl tert-butyl ether field 290 114 10 .04 - .61 39 3.4

Methyl tert-butyl ether trip 112 52 3 .04 - .29 46 2.7

Methylene chloride field 290 192 19 .02 - 13 69 6.6

Methylene chloride trip 112 78 0 .03 - .14 70 0

Naphthalene field 290 38 1 .06 - .21 17 .3

Naphthalene trip 112 10 0 .06 - .13 13 0

n-Propylbenzene field 290 33 4 .05 - .32 11 1.4

n-Propylbenzene trip 112 2 1 .07 - .28 1.8 .9

Styrene field 290 169 58 .03 - 7.9 58 20

Styrene trip 112 48 6 .03 - 1.5 43 5.4

tert-Amyl methyl ether field 287 4 0 .04 - .07 1.4 0

tert-Amyl methyl ether trip 112 1 0 .04 0.9 0

1,1,2,2-Tetrachloroethane field 290 2 0 .06 - .09 0.7 0

1,1,2,2-Tetrachloroethane trip 112 0 0 not detected 0 0

Tetrachloroethene field 290 9 2 .05 - 12 3.1 .7

Tetrachloroethene trip 112 0 0 not detected 0 0

Table 5. Volatile organic compounds detected in field and trip blanks–Continued

[MDL, method detection limit; MRL, minimum reporting level, μg/L, microgram per liter]

Volatile organic 

compound

Blank Number of 

detections Range of 

concentration 

(μg/L)

Frequency of detection

(percent)

Type Number

At or

 above

 MDL

At or

 above

 MRL

At or above 

the MDL

At or above 

the MRL
Data Collection and Analysis 17

Toluene field 290 208 36 0.03 - 3.4 74 12

Toluene trip 112 57 2 .03 - 1.7 51 1.8

1,2,3-Trichlorobenzene field 290 12 0 .05 - .11 4.8 0

1,2,3-Trichlorobenzene trip 112 1 0 .07 1.8 0

1,2,4-Trichlorobenzene field 290 14 0 .04 - .16 4.8 0

1,2,4-Trichlorobenzene trip 112 5 0 .06 - .12 4.5 0

1,1,1-Trichloroethane field 290 2 1 .15 - .52 .7 .3

1,1,1-Trichloroethane trip 112 0 0 not detected 0 0

1,1,2-Trichloroethane field 290 5 0 .02 - .07 1.7 0

1,1,2-Trichloroethane trip 112 0 0 not detected 0 0

Trichloroethene field 290 7 3 .04 - 2.9 2.4 1.0

Trichloroethene trip 112 0 0 not detected 0 0

Trichlorofluoromethane field 290 5 3 .15 - .28 1.7 1.0

Trichlorofluoromethane trip 112 0 0 not detected 0 0

1,2,4-Trimethylbenzene field 290 32 13 .03 - .58 11 4.5

1,2,4-Trimethylbenzene trip 112 1 0 .03 .9 0

1,3,5-Trimethylbenzene field 290 12 0 .03 - .13 4.1 0

1,3,5-Trimethylbenzene trip 112 0 0 not detected 0 0

Vinyl chloride field 290 1 1 .2 .3 .3

Vinyl chloride trip 112 0 0 not detected 0 0

m-, p-Xylene field 290 119 63 .07 - 4.0 41 22

m-, p-Xylene trip 112 12 3 .07 - 2.3 11 2.7

o-Xylene field 290 93 31 .03 - 2.1 32 11

o-Xylene trip 112 7 1 .03 - 1.5 6.2 .9

Table 5. Volatile organic compounds detected in field and trip blanks–Continued

[MDL, method detection limit; MRL, minimum reporting level, μg/L, microgram per liter]

Volatile organic 

compound

Blank Number of 

detections Range of 

concentration 

(μg/L)

Frequency of detection

(percent)

Type Number

At or

 above

 MDL

At or

 above

 MRL

At or above 

the MDL

At or above 

the MRL
18 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Figure 4. Concentrations of methyl tert-butyl ether (MTBE) in all source-water and field quality-control samples

analyzed for the Random Survey, plotted sequentially by date and time of analysis.

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

>2.2

1 100 199 298 397 496 595 694 793 892 991 1090 1189 1288

SAMPLE NUMBER IN ANALYTICAL SEQUENCE

MTBE CONCENTRATION, IN MICROGRAMS PER LITER

Figure 5. Concentrations of naphthalene in all source-water and field quality-control samples analyzed for the

Random Survey, plotted sequentially by date and time of analysis.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3

1 100 199 298 397 496 595 694 793 892 991 1090 1189 1288

SAMPLE NUMBER IN ANALYTICAL SEQUENCE

NAPHTHALENE CONCENTRATION, IN MICROGRAMS PER LITER
Data Collection and Analysis 19

Next, the concentration of all VOCs detected in 

source-water samples were plotted against the concentration of these VOCs in companion FRBs. An example 

of these plots for m-, p-xylene is shown in figure 6. The 

x-y plots readily identify samples that contain similar 

concentrations of the same analyte in both source water 

and FRBs. Nearly equal concentrations in the sourcewater sample and the field blank may result from 

simultaneous contamination of the sample and the 

blank from an external source. For example, figure 6 

shows 18 pairs of source-water samples and FRBs containing concentrations of m-, p-xylene that plot on or 

close to a 1:1-ratio line. Because the data do not demonstrate a constant bias in one direction, that is, the 

source-water concentrations are not always greater 

than the FRBs, the process that caused contamination 

of the samples must have been random rather than systematic. Consequently, it is impossible to develop an 

algorithm to “correct” sample concentrations back to 

“original” concentrations, but it is necessary to quantify the maximum potential extent of random contamination with respect to reporting the frequency of VOC 

detection in source water.

An analysis of source-water detections, together 

with the QC data, can be used to identify and adjust the 

frequency of detection for the possibility of random 

sample contamination. First, the data for the sourcewater samples are subdivided into seven categories (lettered A-D, E1, E2, and F in fig. 7) that relate to the level 

of uncertainty associated with the validity of VOC 

detections. Five of the seven categories (A-D and E1) 

reflect valid results with no random contamination 

uncertainty (see fig. 7); however, two groups (E2 and F) 

include measurable and undeterminable (estimated) 

levels of uncertainty, with regard to random contamination. The lack of VOC detections clearly demonstrates 

the absence of sample contamination at the MRL. Conditions A, B, and C showed no VOC detections above 

the MRL, and although detections were noted in the 

FRBs for condition B, the results from these groups 

Figure 6. Comparison of concentrations of m-, p-xylenes in source-water samples and companion field blanks.

0

0.5

1.0

1.5

2.0

2.5

3.0

0 0.5 1.0 1.5 2.0 2.5 3.0

m-, p-XYLENE CONCENTRATION IN FIELD BLANKS,

IN MICROGRAMS PER LITER

m-, p-XYLENE CONCENTRATION IN SOURCE WATER, IN MICROGRAMS PER LITER

1:1FIELD BLANK: SOURCE WATER
20 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

were considered to accurately represent the sourcewater conditions. Similarly, the results for condition D, 

in which VOCs were detected in the source water and 

the corresponding FRBs were clean (that is, no VOCs 

detected), also are considered valid VOC detections 

because there is no indication of contamination in the 

FRBs. The validity of two groups of data remain in 

question: (1) samples that have the same VOCs in the 

source water and companion field blanks (conditions 

E1 and E2), and (2) those source-water samples with 

concentrations of VOC analytes that do not have 

corresponding FRBs (condition F). 

Figure 7. Schematic diagram for adjusting the frequency of detection of volatile organic compounds (VOCs) in source-water 

samples to reflect possible random sample contamination.

POSSIBILITY OF RANDOM

CONTAMINATION OF

SOURCE-WATER SAMPLES

CONDITION

(MTBE, methyl tert-butyl ether)

No random sample contamination Condition A: Source water = no VOCs detected

Field reagent blank = no VOCs detected

For MTBE = 189 samples

No random sample contamination Condition B: Source water = no VOCs detected

Field reagent blank = VOCs detected

For MTBE = 4 samples

No random sample contamination Condition C: Source water = no VOCs detected

Field reagent blank = not analyzed

For MTBE = 662 samples

No random sample contamination Condition D: Source water = VOCs detected

Field reagent blank = no VOCs detected

For MTBE = 77 samples

No random sample contamination Condition E1: Source water = VOCs detected

Field reagent blank = same VOCs detected, and

source-water concentrations are >5 times

field reagent-blank concentrations

For MTBE = 0 samples

 Random sample contamination suspected Condition E2: Source water = VOCs detected

Field reagent blank = same VOCs detected, and

source-water concentrations are < 5 times

field reagent-blank concentrations

For MTBE = 20 samples

Undetermined possibility of random sample

contamination

Condition F: Source water = VOCs detected

Field reagent blank = not analyzed

For MTBE = 4 samples

Frequency of detection, unadjusted = D+E1+E2+F/A+B+C+D+E1+E2+F

for MTBE = (77+0+20+4)/(189+4+662+77+0+20+4) = 101/956 = 10.6 percent

Frequency of detection, adjusted = C+E1+F/A+B+C+D+E1+F

 for MTBE = (77+0+4)/(189+4+662+77+0+4) = 81/936 = 8.7 percent

Estimated frequency of detection that may be attributed to random contamination of source-water samples = frequency of 

detection, unadjusted - frequency of detection, adjusted for MTBE = 10.6 percent - 8.7 percent = 1.9 percent
Data Collection and Analysis 21

The data for samples with detections of the same 

VOCs in both the source-water sample and the companion FRB (condition E) were examined and divided 

into two subcategories—source-water detections that 

were greater than (condition E1) or less than (condition 

E2) five times the concentration in the FRB (table 6). 

Source-water samples with five or more times the concentrations of VOCs measured in FRBs were judged to 

have virtually no possibility that the source-water concentration was an artifact of random contamination. 

These samples were rare—only one source-water 

detection for chloroform, bromodichloro-methane, and 

bromoform met this criteria. For samples with VOCs at 

concentrations less than five times the FRB concentration, there was clear possibility that the source-water 

detection was due to random contamination, particularly when concentrations approached a 1:1 ratio for 

one or more contaminant. Accordingly, 153 sourcewater VOC detections that fell under condition E2 were 

removed from the source-water dataset and are not 

included in the occurrence of VOCs in source water 

provided in this report. This is a conservative approach 

to reporting VOC occurrence, and the author recognizes 

that the occurrence of the same VOCs in a source-water 

sample and its companion field blank does not indicate 

definitively that random contamination of the sourcewater sample has occurred, but rather only that contamination cannot definitively be ruled out. 

Detection of VOCs in FRBs and TRBs confirms 

contamination of the blank water at some time subsequent to shipment from the MWDSC laboratory. Such 

contamination has been observed in FRBs without contamination of companion source-water samples (condition B). It is for this reason that the source-water 

samples with VOC detections but without companion 

FRBs (condition F) are considered to have some uncertainty associated with the validity of these detections 

but are not censored from the source-water data in subsequent analysis of the occurrence of VOCs.

The process used to identify source-water samples that may have been affected by random VOC 

contamination is summarized in figure 7, and VOCdetection frequencies are adjusted accordingly. The 

adjusted detection frequency is equal to the total 

number of times a VOC was detected at the MRL minus 

the number of condition E2 samples (samples with 

VOC concentrations less than 5 times those in the corresponding FRBs), divided by the total number of 

samples minus the number of condition E2 samples. 

The difference between the adjusted detection frequency and the unadjusted detection frequency represents the possible extent of random contamination of 

source-water samples. The frequency of detection was 

adjusted downward for 20 of the 42 VOCs detected in 

source-water samples because some of the VOC 

detections may be from random contamination. 

Differences between the unadjusted frequency 

of detection in source-water samples and the frequency of detection adjusted for possible random contamination range from 2.3 percent for toluene to 0.1 

percent for several VOCs, but are zero for more than 

half of the 42 VOCs detected in source water (table 7). 

Random contamination may account for 1 percent or 

more of the unadjusted detection frequency for seven 

VOCs including toluene, styrene, m-, p-xylene, 

MTBE, o-xylene, ethylbenzene, and 1,2,4-trimethylbenzene. Consequently, for this report, the detection 

frequency of VOCs at concentrations equal to or 

exceeding the MRL in source water can be most confidently and conservatively reported to be equal to the 

adjusted detection frequency. Accordingly, for 

example, it is reported that 8.7 percent of the sourcewater samples contained the gasoline additive MTBE 

at concentrations equal to or exceeding 0.2 μg/L, even 

though as many as 10.6 percent of sources may have 

contained MTBE.

Finally, a review of data for the TRBs was conducted to determine if there was a relation between the 

frequency and concentration of VOC detections in 

the TRBs and the FRBs for sites where each of these 

field QC samples were collected. Most of the time 

(83 percent of all TRB detections) when VOCs were 

detected in the trip blanks, they also were detected in 

the field blanks. Among the 105 companion trip and 

field blanks that were analyzed by the MWDSC, 

94 percent of the TRB detections were at concentrations less than the MRL. Two-thirds of the time when 

the same compound was detected in both blanks, the 

concentration in the TRB was less than in the FRB. A 

statistical analysis (Wilcoxon signed-rank test) of the 

relation between TRB and FRB concentrations indicated that concentrations of 10 of the 20 VOCs 

detected in both blanks were significantly greater (at 

the 95-percent confidence level) in FRBs (table 8).
22 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Table 6. Number of source-water samples that meet specified conditions with respect to the possibility 

of random contamination

Volatile organic

 compound

Condition (see fig. 7) and number of samples

 A B C D E1 E2 F

Chloroform 172 2 654 107 1 8 12

Methyl tert-butyl ether 189 4 662 77 0 20 4

Bromodichloromethane 233 1 660 54 1 1 6

Chlorodibromomethane 242 1 659 46 0 1 7

Toluene 239 18 666 10 0 23 0

Bromoform 261 1 661 27 1 0 5

Tetrachloroethene 262 0 665 26 0 2 1

m-, p-Xylene 220 44 665 6 0 20 1

Styrene 225 40 665 4 0 21 1

Trichloroethene 264 1 666 22 0 2 0

o-Xylene 252 17 665 5 0 16 1

Ethylbenzene 251 20 665 4 0 15 1

1,2,4-Trimethylbenzene 273 4 666 4 0 9 0

cis-1,2-Dichloroethene 278 0 666 12 0 0 0

1,1-Dichloroethane 279 0 666 11 0 0 0

1,1,1-Trichloroethane 280 0 665 9 0 1 1

Isopropylbenzene 276 5 666 2 0 7 0

1,1-Dichloroethene 283 0 665 7 0 0 1

Carbon tetrachloride 283 0 666 7 0 0 0

Methyl ethyl ketone 285 3 666 5 0 1 0

Trichlorofluoromethane 282 3 666 5 0 0 0

Methylene chloride 268 18 665 2 0 2 1

Benzene 284 2 666 3 0 1 0

1,4-Dichlorobenzene 285 2 665 2 0 1 1 

Dichlorodifluoromethane 285 2 666 4 0 0 0

Chloromethane 286 2 665 2 0 0 1

1,2-Dichloroethane 287 0 666 3 0 0 0

Dibromomethane 270 0 645 2 0 0 0

1,2-Dichloropropane 275 0 645 1 0 1 0

Naphthalene 287 1 666 2 0 0 0 

1,1,2-Trichloro-1,2,2-trifluoroethane 288 0 666 2 0 0 0

Bromomethane 289 0 665 1 0 0 1

n-Propylbenzene 285 3 666 1 0 1 0

tert-Amyl methyl ether 285 0 666 2 0 0 0

Diisopropyl ether 288 0 666 2 0 0 0

1,2,3-Trichloropropane 289 0 666 1 0 0 0

Vinyl chloride 288 1 666 1 0 0 0

n-Butylbenzene 289 0 666 1 0 0 0

Ethyl tert-butyl ether 289 0 666 1 0 0 0

Chloroethane 289 0 666 1 0 0 0

Chlorobenzene 289 0 666 1 0 0 0

1,2-Dichlorobenzene 289 0 666 1 0 0 0
Data Collection and Analysis 23

Table 7. Frequency of detection of volatile organic compounds in source-water samples at or above the minimum 

reporting level adjusted for random contamination

Volatile 

organic

 compound

Unadjusted Adjusted

Number of Difference

detections

Number of

samples

Detection 

frequency

Number of 

detections

Number of 

samples

Detection 

frequency

Chloroform 128 956 13.4 120 948 12.7 0.7

Methyl tert-butyl ether 101 956 10.6 81 936 8.7 1.9 

Bromodichloromethane 62 956 6.5 61 955 6.4 0.1 

Chlorodibromomethane 54 956 5.7 53 955 5.6 0.1

Bromoform 33 956 3.4 33 956 3.4 0

Tetrachloroethene 29 956 3.0 27 954 2.8 0.2

Trichloroethene 24 955 2.5 22 953 2.3 0.2 

cis-1,2-Dichloroethene 12 956 1.3 12 956 1.3 0

1,1-Dichloroethane 11 956 1.2 11 956 1.2 0

Toluene 33 956 3.4 10 933 1.1 2.3

1,1,1-Trichloroethane 11 956 1.2 10 955 1.0 0.2

m-, p-Xylene 27 956 2.8 7 936 0.8 2.0

1,1-Dichloroethene 8 956 0.8 8 956 0.8 0

Carbon tetrachloride 7 956 0.7 7 956 0.7 0

o-Xylene 22 956 2.3 6 940 0.6 1.7

Ethylbenzene 20 956 2.1 5 941 0.5 1.6

Methyl ethyl ketone 6 955 0.6 5 954 0.5 0.1 

Trichlorofluoromethane 5 956 0.5 5 956 0.5 0

Styrene 26 956 2.7 5 935 0.5 2.2 

1,2,4-Trimethylbenzene 13 956 1.4 4 947 0.4 1.0 

Dichlorodifluoromethane 4 956 0.4 4 956 0.4 0

Methylene chloride 5 956 0.5 3 954 0.3 0.2

Benzene 4 956 0.4 3 955 0.3 0.1

1,4-Dichlorobenzene 4 956 0.4 3 955 0.3 0.1

Chloromethane 3 956 0.3 3 956 0.3 0

1,2-Dichloroethane 3 956 0.3 3 956 0.3 0

Isopropylbenzene 9 956 0.9 2 949 0.2 0.7

Dibromomethane 2 922 0.2 2 922 0.2 0

Naphthalene 2 956 0.2 2 956 0.2 0 

1,1,2-Trichloro-1,1,2-

trifluoroethane

2 956 0.2 2 956 0.2 0

Bromomethane 2 956 0.2 2 956 0.2 0

tert-Amyl methyl ether 2 956 0.2 2 956 0.2 0

Diisopropyl ether 2 956 0.2 2 956 0.2 0

n-Propylbenzene 2 956 0.2 1 955 0.1 0.1

1,2-Dichloropropane 2 922 0.2 1 921 0.1 0.1 

1,2,3-Trichloropropane 1 956 0.1 1 956 0.1 0

Vinyl chloride 1 956 0.1 1 956 0.1 0

n-Butylbenzene 1 956 0.1 1 956 0.1 0

Ethyl tert-butyl ether 1 956 0.1 1 956 0.1 0

Chloroethane 1 956 0.1 1 956 0.1 0

Chlorobenzene 1 956 0.1 1 956 0.1 0

1,2-Dichlorobenzene 1 956 0.1 1 956 0.1 0
24 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Table 8. Statistical comparison of the concentrations of volatile organic compounds in 105 companion field blanks

and trip blanks

[FRB, field reagent blank; TRB, trip reagent blank; Ho, null hypothesis; <, less than; >, more than; p-values <0.05 significant at 95-percent 

confidence level shown in bold]

Volatile

 organic

 compound

Number of 

detections in 

field blanks

Number of 

detections in 

trip blanks

Null hypothesis tested and p-value

Ho: FRB=TRB Ho: FRB<TRB Ho: FRB>TRB

Toluene 88 54 <0.0001 <0.0001 1.0

Styrene 71 44 <0.0001 <0.0001 1.0

m-, p-Xylene 39 10 <0.0001 <0.0001 1.0

Ethylbenzene 33 8 <0.0001 <0.0001 1.0

o-Xylene 29 6 <0.0001 <0.0001 1.0

Chloroform 36 16 0.0001 0.0001 0.9999

n-Propylbenzene 12 2 0.0037 0.0019 0.9982

Isopropylbenzene 12 2 0.0041 0.0021 0.9980 

1,2,4-Trimethylbenzene 8 1 0.0047 0.0024 0.9977

Methylene chloride 71 75 0.0286 0.0143 0.9858

1,2,3-Trichlorobenzene 3 1 0.0843 0.9589 0.3173

Benzene 6 2 0.1564 0.9228 0.0782

Methyl tert-butyl ether 42 48 0.2282 0.8866 0.1141

1,2,4-Trichlorobenzene 4 4 0.3173 0.8437 0.1587

Bromobenzene 0 1 0.3219 0.1610 0.8436

1,4-Dichlorobenzene 1 1 0.3219 0.1610 0.8436

tert-Amyl methyl ether 0 1 0.3219 0.1610 0.8436

Naphthalene 11 9 0.7948 0.2068 0.1564

1,3-Dichloropropane 1 1 1.0 0.5054 0.5000

p-Isopropyltoluene 1 1 1.0 0.5027 0.5027

Larger concentrations of VOCs in FRBs than in TRBs 

may indicate that the source of contamination for these 

compounds was present at the source-water site, as the 

field blanks were opened to the atmosphere only at 

those locations, whereas the trip blanks were not. There 

were too few (less than 10) detections for eight VOC 

analytes (table 8) to discern differences between the 

FRB and TRB concentrations for these compounds. For 

MTBE and naphthalene, there were sufficient detections for valid statistical analysis; however, no significant differences were observed in either blank type. 

Consequently, the low-level contamination evident in 

field blanks for MTBE and naphthalene may not be 

field related.

In summary, the review of field QC and sourcewater data suggests that random contamination of some 

source-water samples may have occurred for some 

VOC analytes even at concentrations censored at the 

MRL. The strategy ultimately selected to calculate the 

frequency of detection of each analyte in the Random 

Survey was to exclude detections for source-water samples when evidence of possible random contamination 

for that analyte existed (condition E2 in table 6 and fig. 

7). As such, the occurrence of VOCs in source water 

reported by the Random Survey has been adjusted 

downward for the extent of random contamination 

determined from the field QC samples collected as part 

of this survey.
Data Collection and Analysis 25

Collectively, laboratory and field quality-control 

data and the above-noted procedures used to calculate 

VOC detection frequencies provide a high assurance of 

the validity of reported detections. To be included as a 

detection in the Random Survey, a compound tentatively identified from the analysis of a source-water 

sample must have passed all three of the following 

criteria:

• The compound was positively identified via its 

fragmentation pattern;

• Detection of the compound was not due to laboratory contamination; and

• Detection of the compound was not due to field 

contamination.

Collection of Ancillary Information

In addition to source-water and quality-control 

samples, ancillary information was collected from the 

participating CWSs and other sources. This information was needed for statistical analysis and to determine 

possible relations between the occurrence of MTBE or 

other VOCs in the source-water samples and anthropogenic factors. Ancillary information included location 

(latitude and longitude) of the drinking-water sources 

sampled (well or intakes); actual population served by 

the CWS; source-water characteristics (for example, 

well depth, yield, aquifer type, surface-water type and 

size, intake specifics, and any previous water-quality 

problems); areal patterns of MTBE and other fueloxygenate use; land use; population density; and known 

or potential point-source locations of VOCs (toxic 

release inventory sites, leaking underground storage 

tanks, and Resource Conservation and Recovery Act 

and Comprehensive Environmental Response, and 

Compensation and Liability Act regulated sites) near 

the sampled drinking-water sources. This information 

was obtained from available data bases and (or) collected directly from participating CWSs through their 

responses to a mail-in questionnaire.

Information on the precise location of drinkingwater sources often is missing from the SDWIS data 

base; therefore, latitude and longitude information was 

requested from each of the participating CWSs for each 

drinking-water source sampled (intake or well). If latitude and longitude were not available, the CWSs was 

asked to locate the well or intake on a topographic map, 

from which USGS personnel determined the latitude 

and longitude. To confirm latitude and longitude 

locations (if provided) or to determine the location of 

the drinking-water source if not, a follow-up telephone call was made during which the CWS contact 

was asked to verbally describe the location of the well 

or intake to USGS personnel. Latitude and longitude 

was then determined or confirmed using DeLorme 

Street Atlas/Topo USA software (DeLorme, 

Yarmouth, Maine), and it was entered into a geographical information system (GIS). The results of the analysis that use the locational information obtained for 

this study are included in a later section of this report, 

however, the locations of drinking-water sources are 

not releaseable under current (2002) USGS Homeland 

Security policy.

A short questionnaire was filled out during an 

initial telephone interview with CWS staff when they 

agreed to participate in the Random Survey. The initial 

questionnaire was used to verify basic information 

obtained from the SDWIS data base for the selected 

utility, obtain some additional information on the 

source waters to be sampled, and identify the persons 

and means for further contact. A more detailed written 

questionnaire (Ivahnenko and others, 2001, 

appendix A, p. 27-34) was subsequently delivered to 

the CWS with their sample kit. The written questionnaire requested information about the source water, 

intake location, filtration and treatment, distribution 

area, actual population served, and the quality and 

quantity of water delivered by suppliers. Specific 

information requested on the questionnaire included 

well characteristics, aquifer type, vulnerability of 

ground-water sources, and watershed protection and 

watercraft-use characteristics of surface-water 

sources. 

Participation in the mail-in questionnaire survey 

was remarkably high—99 percent of the CWSs participated and 941 responses to the written questionnaire 

were received. The responses to 70 questions posed by 

the questionnaire were tabulated and are presented in 

appendix 1 of this report. This information provides 

valuable insight into environmental conditions and 

operational characteristics of drinking-water sources 

sampled for the Random Survey. To the extent possible, this information will be extrapolated to provide 

support to observations and conclusions regarding the 

occurrence and distribution of MTBE and other VOCs 

in source water. To some degree, however, the utility 

of the ancillary information from the mail-in questionnaire is constrained by the relatively high number of 

responses with missing or ambiguous information for 

some questions (see appendix 1). 
26 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

National geospatial data on land use (Vogelmann 

and others, 2001), population density (Price and 

Clawges, 1999), and point-source locations of VOCs 

(Vista Information Systems, 1999) were used to augment the ancillary information obtained from the mailin questionnaire and to provide a consistent coverage 

for all participating CWSs. Information on MTBE or 

other fuel-oxygenate use was compiled from USEPA 

documentation (U.S. Environmental Protection 

Agency, 1999b; 1999c) and industry surveys. This 

ancillary information was used to identify important 

natural and anthropogenic factors associated with the 

locations of drinking-water sources that relate to the 

frequency and concentration of MTBE and other VOCs 

observed in source water. 

OCCURRENCE AND DISTRIBUTION OF 

VOLATILE ORGANIC COMPOUNDS IN 

DRINKING-WATER SOURCES

The 954 source-water samples collected from 

May 3, 1999 to October 23, 2000 by the participating 

CWSs were analyzed for VOCs by the MWDSC laboratory and are the basis for the findings of the Random 

Survey. The data include analyses for 66 VOCs in 579 

ground-water and 375 surface-water samples (table 4). 

Some samples for six compounds— dibromomethane, 

1,2-dichloropropane, 1,3-dichloropropane, bromochloromethane, trichloroethene, and methyl ethyl ketone— 

did not meet the daily calibration control checks 

(83 times collectively), and consequently, these analytes were not reported by the MWDSC laboratory. 

Also, as discussed previously in this report, a review of 

quality-control data identified 153 VOC detections at 

the MRL that may have resulted from random contamination of source-water samples (condition E2 samples 

in table 6), and these analytical determinations were 

removed from the source-water database. Consequently, 22 analytes were reported in fewer than 

954 source-water samples (see appendix 2). A total 

of 62,728 (99.6 percent) of 62,964 potential VOC 

analytical determinations of the 66 target analytes are 

included in this analysis. 

Forty-two of the 66 target VOC analytes were 

detected in at least 1 source-water sample at a concentration equal to or greater than its MRL. Eleven 

compounds were detected in more than 1.0 percent of 

source-water samples (fig. 8A), whereas 31 VOCs were 

detected in fewer than 1.0 percent of the samples (fig. 

8B). One or more VOCs were detected in 257 

(27 percent) of the 954 source-water samples at concentrations equal to or exceeding the MRL. The 

number of detections at or above the MRL, the frequency of detection at the MRL, and the range of concentrations of all VOCs detected in the source-water 

samples is tabulated by type of source water and size of 

CWS in appendix 2. 

Chloroform was the most frequently detected 

VOC, reported at concentrations equal to or greater 

than 0.2 μg/L in 120 (nearly 13 percent) of the sourcewater samples (fig. 8A). MTBE was the second most 

frequently detected VOC, reported in 81 (8.7 percent) 

of the source waters sampled (fig. 8A). Other VOCs 

detected in 10 or more source-water samples (fig. 8A) 

include three additional trihalomethanes—bromodichloromethane, chlorodibromomethane, and bromoform—several commonly used solvents or their degradation by-products— tetrachloroethene, trichloroethene, cis-1,2-dichloroethene, 1,1-dichloroethane, 

and 1,1,1-trichloroethane—and one other gasoline 

compound, toluene. All other VOCs detected in source 

waters (fig. 8B) were detected rarely (in fewer than 

10 source-water samples).

Although VOCs were detected in about onequarter of the source waters sampled, VOC concentrations were small. About 95 percent of the total 530 

VOC detections reported by the MWDSC laboratory 

were at concentrations less than 10 μg/L, and nearly 

two-thirds of all detections (63 percent) were less than 

1.0 μg/L. However, eight source-water samples contained concentrations of 1,1-dichloroethene, tetrachloroethene, trichloroethene, and (or) vinyl chloride that 

would exceed USEPA’s MCLs if the samples represented finished drinking water. All but one of these 

elevated concentrations were in samples from groundwater sources (one surface-water sample contained 

slightly more than 5 μg/L of tetrachloroethene and one 

other surface-water sample exceeded the total trihalomethane (TTHM) MCL of 80 μg/L. The cumulative 

distribution of the concentrations of VOCs detected in 

source-water samples (fig. 9) shows that concentrations 

were similar in ground water and surface water.
Occurrence and Distribution of VOCs in Drinking-Water Sources 27

Figure 8. Frequency of detection of volatile organic compounds detected in (A) more than 1.0 percent of source-water

samples and (B) less than 1.0 percent of source-water samples.

0

2

4

6

8

10

12

14

FREQUENCY OF DETECTION, IN PERCENT FREQUENCY OF DETECTION, IN PERCENT

Chloroform

Methyl tert-butyl ether

Bromodichloromethane

Chlorodibromomethane

Bromoform

Tetrachloroethene

Trichloroethene

cis-1,2-Dichloroethene

1,1-Dichloroethane

Toluene

1,1,1-Trichloroethane

A

B

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1,1-Dichloroethene

m-, p-Xylene

Carbon tetrachloride

o-Xylene

Styrene

Ethylbenzene

Methyl ethyl ketone

Trichlorofluoromethane

1,2,4-Trimethylbenzene

Dichlorodifluoromethane

Benzene

1,4-Dichlorobenzene

1,2-Dichloroethane

Chloromethane

Dibromomethane

Isopropylbenzene

Methylene chloride

Diisopropyl ether

tert-Amyl methyl ether

Bromomethane

Naphthalene

1,2-Dichloropropane

n-Propylbenzene

1,2,3-Trichloropropane

n-Butylbenzene

Chlorobenzene

1,1,2-Trichloro-1,2,2-trifluoroethane

1,2-Dichlorobenzene

Chloroethane

Ethyl tert-butyl ether

Vinyl chloride
28 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

When VOCs were detected in source-water 

samples, co-occurrence of several VOCs was fairly 

common, with multiple detections in nearly half 

(47 percent) of the 257 samples with VOC detections. 

Ground-water sources were more likely to contain multiple VOCs than surface-water sources (fig. 10), particularly when five or more VOCs occurred together. One 

ground-water sample contained 17 individual compounds and another contained 10 compounds. The 

percent co-occurrence among the 42 VOCs detected in 

source-water samples is equal to the number of times 

compound X also was detected among the samples that 

contained compound Y, multiplied by 100 (appendix 

3). The appendix shows that 46 pairs of VOCs cooccurred at least 20 percent of the time (when 10 or 

more samples contained 1 of the paired VOCs), and that 

17 pairs exhibited co-occurrence 50 percent or more of 

the time. Co-occurrence of VOCs in source-water samples most frequently involved detections of solvents, 

THMs, and gasoline compounds.

Co-occurrence can take place when several 

VOCs have a common source; for example, the presence of several trihalomethanes in a sample may be 

related to disinfection with chlorine, or the co-occurrence of several BTEX compounds suggests a gasoline 

source. A high percentage of co-occurrence also can 

reflect the degradation of parent VOC compounds to 

their by-products, for example, the co-occurrence of 

tetrachloroethene and trichloroethene in 83 and 

91 percent, respectively, of the source-water samples 

that contained cis-1,2-dichloroethene. By contrast, the 

co-occurrence of multiple VOCs from different subgroups, including MTBE, chloroform and other trihalomethanes, and several common solvents in sourcewater samples does not necessarily imply a common 

source for these contaminants. Rather, their frequent 

co-occurrence may be an artifact of their overlapping 

widespread occurrence.

The 42 VOCs detected in source water at concentrations equal to or greater than the MRL are classified 

in table 9 into 6 subgroups based on their most common 

use or probable source relative to their occurrence in 

water. These include (1) disinfection by-products, (2) 

gasoline compounds, (3) solvents, (4) refrigerants, (5) 

VOCs used in the synthesis of other organic chemicals, 

and (6) fumigants. Similarities in the uses and (or) 

Figure 9. Cumulative distribution of concentrations of volatile organic compounds detected in source-water samples

from ground-water and surface-water sources.

0

10

30

20

40

70

60

50

80

90

100

0 1 10 100 1,000

PERCENT OF DETECTIONS

VOLATILE ORGANIC COMPOUND CONCENTRATION, IN MICROGRAMS PER LITER

Ground water

Surface water
Occurrence and Distribution of VOCs in Drinking-Water Sources 29

sources of VOCs in each of the six subgroups may be 

reflected in their occurrence or co-occurrence and their 

distribution. Although most VOCs have numerous uses 

in industry, commerce, and household applications, the 

purpose of identifying a predominant use or source 

subgroup is to facilitate comparisons of their occurrence and distribution by type of source water, size of 

CWSs, as well as by anthropogenic factors later in this 

report. This classification does not imply that other 

uses or sources for specific compounds do not exist. 

Comparison by Type of Source Water and Size 

of Community Water System

Proportionally, slightly more surface-water 

samples (30 percent) than ground-water samples 

(25 percent) contained VOCs, but the differences in 

detection frequency by type of source water were not 

statistically significant for most VOC subgroups 

(table 10). A contingency-table analysis showed that 

gasoline compounds in general, and MTBE in particular, were detected significantly more frequently in surface-water samples than ground-water samples. BTEX 

compounds also were detected more frequently in surface water than in ground water, but the number of 

BTEX detections were too few to demonstrate a 

statistically significant relation with source-water type. 

The elevated detection frequencies for gasoline-related 

VOCs in surface waters may relate to watercraft use on 

the affected water bodies. Because most concentrations 

of gasoline compounds were small, atmospheric and 

(or) storm-water runoff sources also may contribute to 

the more frequent detections (Delzer and others, 1996; 

Lopes and Bender, 1998; Bender and others, 2000). 

Incidents of contamination of ground water from solvents are well-documented, and these compounds were 

detected more frequently in samples from groundwater sources than from surface-water sources in the 

Random Survey, as were the rarely detected chlorofluorocarbon refrigerants. Generally, the number and 

variety of compounds detected were greater for 

ground-water samples than for surface-water samples. 

VOCs would likely be subjected to faster and more 

effective dilution and degradation processes in surface 

water than in ground water. 

Figure 10. Number of volatile organic compounds detected in source-water samples from ground-water and surfacewater sources.

0

40

20

60

100

80

120

140

160

1 23 5 4 6 or more

NUMBER OF SAMPLES

NUMBER OF VOLATILE ORGANIC COMPOUNDS DETECTED PER SAMPLE

Surface water

Ground water
30 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

1

p-value is the attained significance level; values shown in bold are significant at the 95-percent confidence level. 2Source-water type populations that share the same letter are not significantly different at the 95-percent confidence level. 3

Benzene, toluene, ethylbenzene, and m-, o- and p-xylenes.

Table 9. Chemical subgroups of volatile organic compounds detected in source-water samples

Chemical use 

or source

subgroup

Compounds detected

(listed in order of decreasing detection frequency)

Number of

detections

Number

(percent) of

samples with

detections

Disinfection 

by-products

Chloroform, bromodichloromethane, chlorodibromoethane, 

bromoform

265 141 (15)

Gasoline

compounds 

Methyl tert-butyl ether, toluene, m-, p-xylene, o-xylene, ethylbenzene, benzene, diisopropyl ether, tert-amyl methyl ether, 

naphthalene, ethyl tert-butyl ether, n-butylbenzene

120 94 (9.8)

Solvents Tetrachloroethene, trichloroethene, cis-1,2-dichloroethene, 1,1-

dichloroethane, 1,1,1-trichloroethane, 1,1-dichloroethene, 

carbon tetrachloride, methyl ethyl ketone, 1,2-dichloroethane, 

dibromomethane, methylene chloride, 1,2-dichloropropane, 

chlorobenzene, chloroethane, 1,2-dichlorobenzene, n-propylbenzene, 1,2,3-trichloropropane

115 60 (6.3)

Refrigerants Trichlorofluoromethane, dichlorodifluoromethane, 

chloromethane, 1,2,2-trichloro-1,1,2-trifluoroethane

13 10 (1.0)

Organic synthesis 

compounds

Styrene, 1,2,4-trimethylbenzene, isopropylbenzene, 

vinyl chloride

12 10 (1.0)

Fumigants 1,4-dichlorobenzene, bromomethane 5 5 (0.5)

Table 10. Statistical comparison of the occurrence of volatile organic compounds in source-water samples 

by type of source water

[<, less than]

Volatile organic compound,

subgroup, or

related compounds

p-value1

Type of source water and frequency of detection (population2)

Percentage of 

surface-water samples

Percentage of 

ground-water samples

Any volatile organic compound 0.1567 30 (A) 25 (A)

Trihalomethanes 0.6086 14 (A) 16 (A)

Non-trihalomethane compounds 0.113 18 (A) 14 (A)

Any gasoline compound <0.0001 15 (B) 6.6 (A)

Methyl tert-butyl ether <0.0001 14 (B) 5.4 (A)

BTEX3 compounds 0.4877 2.4 (A) 1.6 (A)

Solvents 0.0001 2.4 (A) 8.8 (B)

Refrigerants 0.0256 0 (A) 1.7 (B)

Fumigants 0.6236 .8 (A) .3 (A)

Organic synthesis compounds 0.3071 1.6 (A) .7 (A)
Occurrence and Distribution of VOCs in Drinking-Water Sources 31

For most VOC subgroups, detections were more 

frequent in samples from the very large water systems 

(table 11), particularly for ground-water sources. A 

contingency-table analysis of detection frequencies in 

surface-water sources by size category, however, found 

few significant differences at the 95-percent confidence level. Overall, the frequency of detecting any 

VOC at or above the MRL was greatest (42 percent) in 

ground-water sources used by the very large systems 

(table 11) followed by (33 percent) surface-water 

sources for medium-sized systems. However, VOCs 

were detected in nearly 20 percent or more of sourcewater samples for all source-size categories. Although 

detections of any VOC collectively were significantly 

more frequent in ground-water sources of very large 

CWSs than in ground water supplying very small, 

small, and medium-sized CWSs, the p-value for this 

comparison is even more significant when the four 

trihalomethane compounds are removed and only nontrihalomethane compound detections are compared 

(see table 11). Detections of any gasoline compound, 

solvent, and refrigerant also were significantly more 

frequent in ground-water sources to very large CWSs 

(table 11) than in ground-water sources of smallersized CWSs.

1

p-value is the attained significance level; values shown in bold are significant at the 95-percent confidence level. 2

Source-size populations that share the same letter symbol are not significantly different at the 95-percent confidence level. 3

Benzene, toluene, ethylbenzene, and m-, o- and p-xylenes.

Table 11. Statistical comparison of the occurrence of volatile organic compounds in source-water samples 

by type of source water and size of community water systems

[CWSs, community water systems]

Volatile organic compound or 

related compounds

Type of source 

water p-value1 Size of CWSs and frequency of detection (population)2

Very small Small Medium Large Very large

Any volatile organic compound Ground water

Surface water

0.0381

0.7714

26 (A)

25 (A)

20 (A)

19 (A)

20 (A)

33 (A)

24 (AB)

29 (A)

42 (B)

31 (A)

Trihalomethanes Ground water

Surface water

0.4030

0.4635

18 (A)

8.3 (A)

13 (A)

16 (A)

12 (A)

24 (A)

9.5 (A)

16 (A)

17 (A)

12 (A)

Non-trihalomethane volatile 

organic compounds

Ground water

Surface water

0.0001

0.2190

11 (A)

17 (A)

12 (A)

3.8 (A)

10 (A)

17 (A)

19 (AB)

15 (A)

36 (B)

22 (A)

Any gasoline compound Ground water

Surface water

0.0466

0.1414

5.8 (A)

8.3 (A)

5.0 (AB)

0 (A)

2.0 (A)

13 (A)

9.5 (AB)

14 (A)

15 (B)

18 (A)

Methyl tert-butyl ether Ground water

Surface water

0.0511

0.1054

4.8 (A)

8.3 (A)

3.4 (A)

0 (A)

2.0 (A)

6.7 (A)

8.2 (A)

13 (A)

13 (A)

17 (A)

BTEX3 compounds Ground water

Surface water

0.5642

0.0678

1.7 (A)

0 (A)

0.8 (A)

0 (A)

0 (A)

10 (A)

1.6 (A)

2.5 (A)

3.8 (A)

1.8 (A)

Solvents Ground water

Surface water

<0.0001

0.2687

4.1 (A)

8.3 (A)

8.3 (AB)

0 (A)

8.0 (AB)

6.7 (A)

14 (BC)

2.5 (A)

30 (C)

1.8 (A)

Refrigerants Ground water

Surface water

0.0002

1.0000

1.4 (A)

0 (A)

0 (A)

0 (A)

2.0 (AB)

0 (A)

0 (AB)

0 (A)

9.4 (B)

0 (A)

Fumigants Ground water

Surface water

0.3572

0.7450

0.3 (A)

0 (A)

0 (A)

0 (A)

0 (A)

0 (A)

0 (A)

0 (A)

1.9 (A)

1.3 (A)

Organic synthesis compounds Ground water

Surface water

0.0619

0.0245

0.7 (A)

8.3 (AB)

0 (A)

3.8 (AB)

0 (A)

6.7 (B)

0 (A)

1.3 (AB)

3.8 (A)

0.4 (A)
32 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

The more frequent occurrence of VOCs in source 

waters used by larger CWSs likely reflects the greater 

proximity of drinking-water sources for larger systems 

to high-population density, urban areas compared to the 

locations of drinking-water sources for the smaller 

CWSs (fig. 11). Urban land use and high-population 

density have been shown to be related to increased 

VOC detection frequencies in a number of previous 

studies (Reiser and O’Brien, 1998; Grady, 1994; Grady 

and Mullaney, 1998; Squillace and others, 1999; Bush 

and others, 2000). The relations between the occurrence of VOCs and population density and urban land 

use are evaluated further in a later section of this report. 

Trihalomethane Disinfection By-Products

Four trihalomethane compounds—chloroform, 

bromodichloromethane, chlorodibromomethane, and 

bromoform—are among the by-products commonly 

generated by the disinfection of drinking-water supplies with chlorine and (or) bromine. The four THM 

compounds were among the five most frequently 

detected VOCs in the source-water samples (fig. 8A) 

and, collectively, were detected in 14 percent of the 

surface-water sources and in 16 percent of the groundwater sources (table 10). Detections of chloroform and 

bromodichloromethane (fig. 12) were slightly more 

common in source-water samples from rivers than in 

samples from ground water or reservoirs, but detection 

frequencies of all four THMs were comparable (that is, 

not significantly different) among the three sourcewater types. Furthermore, the frequency of detection of 

THMs was not particularly related to CWS size—proportionally, just as many source-water samples from 

very small ground-water systems had THM detections 

as did samples from the very large ground-water 

systems (table 11), and medium-sized surface-water 

CWSs reported the most frequent THM detections 

among the surface-water sources. 

Because the Random Survey specifically targeted untreated source waters, the widespread occurrence of THMs was not anticipated. The presence of 

THMs and other disinfectant by-products in finished 

drinking water has been well-documented (Westrick, 

Figure 11. Relation between size of community water systems and percentage of drinking-water sources in urban

areas.

0

20

10

30

50

40

60

70

80

PERCENT OF DRINKING-WATER SOURCES IN URBAN AREAS

Very small Small Medium Very large Large

SIZE OF COMMUNITY WATER SYSTEMS

Surface water

Ground water
Occurrence and Distribution of VOCs in Drinking-Water Sources 33

1990; Minear and Amy, 1995; Pomes and others, 

1999). Grady and Casey (2001) reported that drinking 

water supplied by nearly half of all CWSs surveyed in 

that study contained one or more of the four THMs. 

Indeed, drinking-water suppliers are required to maintain sufficient chlorine residual levels in their waterdistribution systems to prevent the existence of waterborne pathogens. It is possible that samplers from some 

of the participating CWSs misinterpreted the samplecollection instructions and collected finished-water 

samples rather than source-water samples. Alternatively, some CWSs report that they back flush their 

filters with chlorinated water that is discharged back 

into the source waters. The cause of the anomalous 

occurrence of concentrations of the total of the four 

trihalomethane compounds (THMs) in excess of 

20 μg/L in nine source-water samples and in excess of 

the 80-μg/L MCL in one sample (fig. 13) is undetermined. 

Chloroform in source waters could originate 

from sources other than a by-product of disinfection, 

including manufacture of pharmaceuticals, dry 

cleaning, fire extinguishers, and fumigants. However, 

chloroform frequently co-occurred in source-water 

samples with other THMs in the following proportions: 

chloroform > bromodichloromethane > chlorodibromomethane > bromoform. THMs in chlorinated water 

typically are present in the same proportions. An explanation for widespread low-level THM detections in 

source waters is that they may represent residual concentrations of disinfectant by-products that formed initially at water or wastewater-treatment plants. Disinfectant by-product residuals persist in the environment 

from irrigation of lawns and parks, sewer exfiltration, 

and treatment-plant effluents. They circulate in surface 

water and ground water until intercepted by watersupply intakes and are detected in the source-water 

samples. Ambient ground water was reported to frequently contain THMs, particularly chloroform, that 

was attributed to infiltration of treated water used to 

water lawns or from leaky water and sewer lines, but 

median concentrations were less than 1.0 μg/L 

(Squillace and others, 1999). THM concentrations 

measured in the source-water samples were similar, 

Figure 12. Frequency of detection of trihalomethanes in source-water samples from ground water, rivers, and

reservoirs (populations that share the same letter symbol are not significantly different at the 95-percent confidence

level).

0

20

10

30

50

40

60

70

80

Chloroform Bromodichloromethance Chlorodibromomethane Bromoform

FREQUENCY OF DETECTION, IN PERCENT

A

A

A

A

A

A

A

A A A

A

A

Ground water

Rivers

Reservoirs
34 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

and were not significantly different among the three 

source-water types (fig. 13). The median concentration 

of TTHMs in ground-water sources (0.86 μg/L) was 

comparable to the 2.5-μg/L median reported by Grady 

and Casey (2001, p. 36) for finished drinking water 

from ground-water supplied CWSs. Median concentrations of TTHMs in surface-water sources (fig. 13), 

however, were substantially lower than the elevated 

median TTHM concentrations of 20 to 30 μg/L 

reported by Grady and Casey (2001, p. 36) in finished 

drinking water from surface-water supplied CWSs.

The temporal distribution of THM detections 

also was examined to determine if any seasonal patterns 

were evident for any particular source-water type. 

Although substantial differences in the frequency of 

THM detections from month to month were found in 

both ground-water and surface-water samples, these 

variations appear to be random. THM detections were 

somewhat less frequent in most summer months (May 

through August) than in other months of the year in 

both ground- and surface-water sources, but with 

variations of nearly an order of magnitude (for 

example, surface-water detections in 2.9 percent of 

samples in May and in 26 percent of samples in June), 

no systematic seasonal pattern is evident in the data 

(fig. 14). 

Figure 13. Concentrations of total trihalomethanes in source-water samples from ground water, rivers, and

reservoirs. TOTAL TRIHALOMETHANE CONCENTRATION, IN MICROGRAMS PER LITER

Ground Water Reservoirs Rivers

SOURCE TYPE

1

0.1

10

100

1,000

p = 0.2725

A

N = 97

median = 0.86

A

A

N = 27 N = 34

median = 1.4

median = 0.46

NUMBER OF DETECTIONS

ATTAINED SIGNIFICANCE LEVEL

POPULATIONS THAT SHARE THE SAME LETTER

 SYMBOL ARE NOT SIGNIFICANTLY DIFFERENT

 AT THE 95-PERCENT CONFIDENCE LEVEL 

N = 97

p = 0.2725

A

EXPLANATION
Occurrence and Distribution of VOCs in Drinking-Water Sources 35

MTBE and Other Gasoline Compounds

Gasoline compounds were the second most frequently detected subgroup of VOCs and were measured in 9.8 percent of the source-water samples 

(table 9). MTBE alone accounted for two-thirds of all 

gasoline-compound detections (8.7 percent of the 

source-water samples), and was the second most frequently detected VOC in source waters after chloroform (fig. 8A). Ten additional VOCs that are intrinsic 

components of gasoline, such as benzene, toluene, 

ethylbenzene, and xylenes (BTEX), or are additives to 

gasoline (including the oxygenates ETBE, DIPE, and 

TAME), also were detected in source-water samples 

(table 9). 

MTBE detections were significantly more frequent (table 10) in surface-water sources (14 percent) 

than in ground-water sources (5.4 percent), and river 

and reservoir samples contained MTBE more than 

twice as often as ground water (fig. 15). The occurrence 

of MTBE in 5.4 percent of ground-water sources in the 

Random Survey matched that observed in the national 

assessment of ambient ground water by Squillace and 

others (1999), also conducted at the same 0.2-μg/L 

MRL. However, Grady and Casey (2001) observed 

more frequent detections of MTBE in finished drinking 

water from CWSs in the Northeast. In that study, 7.8 

percent of CWSs that used ground-water sources exclusively reported MTBE in drinking water (at a 1.0-μg/L 

MRL), whereas only 2.8 percent of these systems that 

use only surface-water sources had reported MTBE. 

CWSs in the Northeast that used both ground-water 

and surface-water sources, however, reported MTBE 

more frequently, in 16-percent of the multiple-source 

systems (Grady and Casey, 2001, p. 38). Toluene was 

the only other gasoline compound detected significantly more frequently in surface water than in ground 

water (p=0.0309), and it was detected six times more 

frequently in rivers than in ground water (fig. 15). Consistent with findings from Grady and Casey (2001), 

MTBE and other gasoline compounds generally were 

detected more frequently in the large CWSs regardless 

of type of source water (table 11). 

Although widely detected, most MTBE concentrations measured in source-water samples were less 

than 5.0 μg/L, and median concentrations were less 

than 1.0 μg/L for each source-water type (fig.16). The 

largest MTBE concentration measured, 20 μg/L, was in 

a source-water sample from a reservoir in California, 

and equalled the lower value of the USEPA’s 

Figure 14. Frequency of detection of trihalomethanes in ground- and surface-water systems by month.

0

10

5

15

25

20

30

35

FREQUENCY OF DETECTION OF TRIHALOMETHANES,

IN PERCENT

JAN FEB MAR APR MAY JUNE JULY AUG SEP OCT NOV DEC

Ground water

Surface water
36 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

recommended drinking-water advisory range for 

drinking water of 20 to 40 μg/L (U.S. Environmental 

Protection Agency, 1997a). The operators of that CWS 

reported that numerous two-stroke, motorized personal 

watercraft use the reservoir for recreational purposes. 

MTBE concentrations did not differ significantly 

between ground-water and reservoir samples (fig. 16), 

but both were significantly greater than river samples. 

It is possible that the lower concentrations observed in 

river source-water samples is because mixing and dilution of gasoline contaminants is more effective in 

flowing water than stratified water bodies, or it may be 

that the rivers in this survey collectively receive less 

motorized watercraft use.

BTEX and other gasoline-related VOCs were 

detected only rarely in source waters (fig. 15) and even 

more rarely together with MTBE (fig. 17). Co-occurring detections of any BTEX compound with MTBE 

occurred in only 10 of 934 (1.1 percent) sourcewater samples. When MTBE was detected, BTEX 

compounds also were detected 12 percent of the time, 

but nearly 30 percent of the 34 source-water samples 

that contained BTEX compounds also contained 

MTBE. Most of the time when these two gasoline components co-occurred, and particularly when the concentrations of MTBE and BTEX were similar (fig. 17), the 

concentrations were low (less than 2.0 μg/L). The few 

MTBE detections that exceeded 2.0 μg/L were largely 

without BTEX in source-water samples. The lack of 

substantial co-occurrence of MTBE and BTEX likely 

reflects the different chemical properties that cause 

MTBE to be relatively persistent in the environment 

compared to BTEX, especially in ground water. Conversely, the ether oxygenates ETBE, DIPE, and TAME, 

while rare (they were detected only in two groundwater samples), were detected only where MTBE also 

was detected. The chemical properties of these compounds are similar to those of MTBE, and they are 

likely present in oxygenated gasoline as impurities or 

alteration products.

Figure 15. Frequency of detection of gasoline compounds in source-water samples from ground water, rivers, and

reservoirs.

0

4

2

6

10

8

12

14

16

FREQUENCY OF DETECTION, IN PERCENT

Toluene

Methyl tert-butyl ether

m- & p-Xylenes

o-Xylene

Ethylbenzene

Benzene

Diisopropyl ether

tert-Amyl methyl ether

Naphthalene

Ethyl tert-butyl ether

n-Butylbenzene

Ground water

Rivers

Reservoirs
Occurrence and Distribution of VOCs in Drinking-Water Sources 37

The temporal distribution of MTBE detections

in ground-water sources and surface-water sources 

(fig. 18) demonstrates substantial differences. 

Although detection frequency varied randomly and no 

seasonal pattern is evident in the detection of MTBE in 

ground water, a seasonal influence seems apparent in 

the surface-water detections. MTBE detection frequency in surface-water samples increases almost 

monotonically from January to June and then similarly 

declines through October (fig. 18). This pattern may 

reflect the seasonal use of watercraft on surface-water 

bodies that are drinking-water sources. Emissions from 

gasoline-powered watercraft, and from personal recreation watercraft equipped with two-stroke engines in 

particular, have been associated with MTBE and BTEX 

contamination of surface waters (Juttner and others, 

1995; Boughton and Lico, 1998; Reuter and others, 

1998; Zapecza and Baehr, 1999; Dale and others, 2000; 

Gabele and Pyle, 2000).

Figure 16. Concentrations of methyl tert-butyl ether (MTBE) in source-water samples from ground water, rivers,

and reservoirs. MTBE CONCENTRATION, IN MICROGRAMS PER LITER

Ground Water Reservoirs Rivers

SOURCE TYPE

1

0.1

10

100

p = 0.0143

N = 31 N = 26 N = 24

NUMBER OF DETECTIONS

ATTAINED SIGNIFICANCE LEVEL

POPULATIONS THAT SHARE THE SAME LETTER

 SYMBOL ARE NOT SIGNIFICANTLY DIFFERENT

 AT THE 95-PERCENT CONFIDENCE LEVEL 

N = 31

p = 0.0143

A

EXPLANATION

median = 0.32

median = 0.71 median = 0.67

B B

A
38 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Figure 17. Comparison of concentrations of methyl tert-butyl ether (MTBE) to the sum of the concentrations of

benzene, toluene, ethylbenzene, and xylene (BTEX) in 934 source-water samples.

0

0 2 4 6 8 10 12 14 16 18 20

8

6

4

2

10

14

12

16

18

20

MTBE CONCENTRATION, IN MICROGRAMS PER LITER

BTEX CONCENTRATION, IN MICROGRAMS PER LITER

1:1 MTBE:BTEX

Figure 18. Frequency of detection of methyl tert-butyl ether (MTBE) in source-water samples from ground-water and

surface-water sources by month.

0

5

10

20

15

25

30

35

FREQUENCY OF DETECTION OF MTBE, IN PERCENT

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Surface water

Ground water
Occurrence and Distribution of VOCs in Drinking-Water Sources 39

Solvents and Other Volatile Organic Compounds

Solvents were the third most frequently detected 

subgroup of VOCs in drinking-water sources, present 

in 6.3 percent of the samples (table 9). Among the 17 

chlorinated solvents detected in source-water samples 

(fig. 19) are several chemicals that have widespread 

industrial and commercial applications (for example, 

dry cleaning, textile production, and metal degreasing 

in automobile-repair and electronic-manufacturing 

facilities). These compounds also are commonly used 

in residential areas in household products such as paint 

strippers, degreasers, aerosols, and adhesives; consequently, solvents have been frequent contaminants in 

ambient ground water (Squillace and others, 1999) and 

in drinking water (Grady and Casey, 2001). 

The occurrence of solvents in drinking-water 

sources is predominantly a ground-water phenomenon, 

as 88 percent of all solvent detections were in groundwater samples. Solvents were detected nearly four 

times more frequently in ground-water sources than in 

surface-water sources. Detection of one or more 

solvents in 8.8 percent of the ground-water samples 

was significantly greater than the 2.4-percent detection 

frequency for surface-water samples (table 10). Detections of 14 solvents were greater in ground water than 

rivers and reservoirs (fig. 19), and more than half of the 

17 solvents detected in source water were present only 

in ground-water samples. Also, solvents were detected 

significantly more often in ground-water sources of the 

largest CWSs (table 11) than in ground-water sources 

of smaller systems. 

Concentrations of solvents in source water were 

somewhat greater than VOCs in general, as 12 percent 

of solvent detections exceeded 10 μg/L compared to 

5 percent for VOCs overall. Concentrations of tetrachloroethene, trichloroethene, and 1,1-dichloroethene 

exceeded drinking-water MCLs (5, 5, and 7 μg/L, 

respectively) 14 times collectively, with a maximum of 

165 μg/L of tetrachloroethene measured in one groundwater sample. The samples were not finished drinking 

water, however, and presumably concentrations of that 

magnitude would be mitigated by some form of 

Figure 19. Frequency of detection of solvents in source-water samples from ground water, rivers, and reservoirs.

0

1.0

0.5

1.5

2.0

3.0

2.5

3.5

4.0

4.5

FREQUENCY OF DETECTION, IN PERCENT

Tetrachloroethene

Trichloroethene

cis-1,2-Dichloroethene

1,1-Dichloroethane

1,1,1-Trichloroethane

1,1-Dichloroethene

Carbon tetrachloride

Methyl ethyl ketone

1,2-Dichloroethane

Dibromomethane

Methylene chloride

1,2-Dichloropropane

Chlorobenzene

Chloroethane

n-Propylbenzene

1,2-Dichlorobenzene

1,2,3-Trichloropropane

Ground water

Rivers

Reservoirs
40 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

treatment or dilution by mixing with other source 

waters prior to distribution. At least 15 percent of the 

CWSs reported using some form of treatment to filter 

or remove VOCs from source waters sampled for this 

study (appendix 1). Overall, most solvent concentrations were not problematic, and the median solvent 

concentration was 1.2 μg/L. Also, perhaps because they 

were present predominantly in ground water or perhaps 

because their sources are widespread and random, 

detections of solvents demonstrated no seasonal patterns.

VOCs other than the trihalomethane disinfectant 

by-products, gasoline compounds, and solvents 

described above have been detected only rarely in 

drinking-water sources. Four refrigerants, four VOCs 

used mostly in the synthesis of other organic chemicals 

or products, and two fumigants were detected in less 

than 1 percent of the source-water samples (table 9). Of 

the three groups of VOCs, only refrigerants demonstrated a distinctive and statistically significant (see 

table 10) difference in their occurrence, as they were 

detected exclusively in ground water (fig. 20). The 

fumigant and organic synthesis VOCs detected in 

source-water samples were present in all source-water 

types but were slightly more prevalent in surface water. 

Anthropogenic Factors Related to Occurrence 

and Distribution 

Anthropogenic factors such as urban land use, 

population density, areas where MTBE use is high, 

and the density of gasoline storage tanks have been 

found to explain, at least in part, the occurrence and 

Figure 20. Frequency of detection of refrigerants, fumigants, and organic synthesis compounds in source-water

samples from ground water, rivers, and reservoirs.

0

0.4

0.2

0.6

0.8

1.0

1.2

1.4

FREQUENCY OF DETECTION, IN PERCENT

Refrigerants Fumigants Organic synthesis

Trichlorofluoromethane

Dichlorodifluoromethane

Chloromethane

1,1,2-Trichloro-1,2,2-trifluoroethane

1,4-Dichlorobenzene

Bromomethane

Styrene

1,2,4-Trimethylbenzene

Isopropylbenzene

Vinyl chloride

Ground water

Rivers

Reservoirs
Occurrence and Distribution of VOCs in Drinking-Water Sources 41

distribution of MTBE and other VOCs in drinking 

water and ambient ground water (Grady, 1994; Delzer 

and others, 1996; Grady and Mullaney, 1998; Hitzig 

and others, 1998; Lopes and Bender, 1998; State of 

Maine, 1998; Moran, Halde and others, 1999; Squillace 

and others, 1999; Squillace and Moran, 2000; Grady 

and Casey, 2001). Consequently, a similar analysis was 

performed for the Random Survey that used information on the location of the drinking-water sources sampled for this study with respect to these anthropogenic 

factors. The locations of the drinking-water sources 

were intersected with national GIS data on 1990 population density (Price and Clawges, 1999) and percentage of urban land use (Vogelmann and others, 

2001) within the four 1-km2 grid cells adjacent to the 

well or intake location. Population density was calculated as an average of the four neighboring grid cells 

weighted for distance of the well or intake from each 

cell. Urban land use was calculated as the percentage of 

total area in the four neighboring cells consisting of 

four land cover types: (1) low-intensity residential, 

(2) high-intensity residential, (3) commercial, industrial, and transportation, and (4) urban recreational 

grasses (for example, parks and golf courses).

High MTBE-use areas were defined as areas 

within the Federal Reformulated Gasoline (RFG) 

Program (U.S. Environmental Protection Agency, 

1999b) whereby gasoline must contain 2-percent 

oxygen by weight and MTBE is the oxygenate of 

choice. Areas designated as “high use” had a median 

content of MTBE in gasoline greater than 9 percent by 

volume in at least one year or season from 1995 through 

1999. Medians of MTBE by volume in gasoline were 

determined from yearly data from the Reformulated 

Gasoline Survey (Stuart Romanow, U.S. Environmental Protection Agency, written commun., 1999) and 

seasonal (winter and summer) data from motor gasoline 

surveys conducted by the National Institute for Petroleum and Energy Research. All areas participating in 

the Federal RFG Program during the April 1999 to 

October 2000 duration of the Random Survey were 

considered high MTBE-use areas, with the exception of 

the Chicago and Milwaukee metropolitan areas, which 

use ethanol in gasoline to meet Federal oxygenate 

requirements. Two areas that were previously in the 

Federal RFG Program also were considered high 

MTBE-use areas for this analysis. Areas of southern 

Maine voluntarily entered (opted into) the RFG Program in 1995 and opted out in 1999. Phoenix, Arizona 

voluntarily entered the RFG Program in 1997 and opted 

out in June 1998. Both of these areas have shown 

significant (>9 percent by volume) MTBE use during 

1995-99.

Two other areas also were considered high 

MTBE-use areas for this analysis, although they did 

not actively participate in the Federal RFG Program. 

All of the State of California, including those areas 

outside RFG Program areas, are considered to be high 

MTBE-use areas because of documented statewide 

use of MTBE to meet the State wintertime oxygenate 

and (or) California Cleaner Gasoline requirements 

(California Environmental Protection Agency, 1997; 

California Senate, 1998; Gomez and others, 1998). 

Additionally, Yuma and Mohave counties in Arizona 

are considered high MTBE-use areas because they 

reportedly receive gasoline containing high MTBE 

content from California gasoline distributors (Arizona 

Department of Environmental Quality, 1999).

The three ancillary factors evaluated—population density, urban land use, and high MTBE-use 

areas—are autocorrelated to some degree. Clearly, 

areas with high population density (greater than 

386 people/km2

 or 1,000 people/mi2) are urban, and 

areas with more than 60 percent total urban land cover 

generally have high population density. Also, because 

the Federal RFG Program was directed at improving 

air quality in places within the country that exceeded 

air-quality standards, due in large part to emissions 

from congested automobile use, these areas typically 

include large urban centers and their surroundings. 

These ancillary factors are only indirect, surrogates 

for quantitative information on VOC sources, use, and 

releases to the environment within urban areas that 

generally is not available. The occurrence and distribution of VOCs in ground water and surface water, 

however, are related to, and to some degree can be 

anticipated by, these factors.

Urban land use within the 4-km2 area surrounding 931 of the 954 drinking-water sources (data 

were not available for Alaska, Hawaii, and Puerto 

Rico) ranged from 0 to 99.9 percent. For this analysis, 

sites were segregated into five categories of urban land 

use corresponding to 0 to 20 percent, 21 to 40 percent, 

41 to 60 percent, 61 to 80 percent, and 81 to 

100 percent urban. The frequency of detection for 

various subgroups of VOCs were statistically compared using contingency-table analysis. The results 

of that analysis demonstrates that the frequency of 

detection of any VOC, non-THM VOCs, BTEX compounds, solvents, and refrigerants was significantly 
42 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

related to urban land use at the 95-percent confidence 

level (table 12). For most of the VOC subgroups, the 

frequency of detection was significantly greater in the 

81- to 100-percent urban land-use categories than in the 

0- to 20-percent urban areas. The relation between 

VOC detections and urban land use can be seen in the 

comparison of the frequency of detection of non-THM 

VOCs for the five urban land-use percentage categories 

(fig. 21)—the frequency of detection of non-THM 

VOCs increased monotonically with increasing urban 

land use and was significantly greater for all areas with 

more than 20 percent urbanization.

A complementary analysis of the relation 

between urban areas and VOC detections in source 

waters was conducted by comparing the frequency 

of detection of each VOC subgroup for areas with 

population density less than and greater than the 

1,000-people/mi2 threshold adopted by Squillace and 

others (1999) to differentiate urban from rural settings. 

Squillace and others (1999) found population density 

to be a stronger explanatory variable than land use in 

statistical models that tested various explanatory factors for the frequency of VOC detections in ambient 

ground water. Similarly to urban land use, the relation 

between detection frequency of any VOC, non-THM 

VOC, solvent, and refrigerant and population density is 

statistically significant (table 13). Unlike urban land 

use, however, detections of any gasoline compound and 

MTBE were significantly greater in drinking-water 

sources from areas of high population density, although 

BTEX compounds were not. MTBE detections were 

almost three times more frequent in high populationdensity areas than in lower population-density areas.

Figure 21. Relation between the frequency of detection of non-trihalomethane volatile organic compounds and urban

land use.

0

15

10

5

20

35

25

30

40

45

50

0-20 21-40 41-60 81-100 61-80

FREQUENCY OF DETECTION, IN PERCENT

URBAN LAND USE, IN PERCENT

ATTAINED SIGNIFICANCE LEVEL

POPULATIONS THAT SHARE THE SAME LETTER

 SYMBOL ARE NOT SIGNIFICANTLY DIFFERENT

p = 0.0143

A

EXPLANATION

p <0.0001 

A

B BC

BC

C
Occurrence and Distribution of VOCs in Drinking-Water Sources 43

1

p-value is the attained significance level; values shown in bold are significant at the 95-percent confidence level.

2

Urban land-use populations that share the same letter are not significantly different at the 95-percent confidence level.

3

Benzene, toluene, ethylbenzene, and o-, m-, and p-xylenes.

Table 12. Statistical comparison of the occurrence of volatile organic compounds in source-water samples by 

percentage of urban land use

[Percentage of urban land use analyzed for four 1-km2 grid cells adjacent to the drinking-water source]

Volatile organic 

compound or related 

compounds

p-value1

Percentage urban land use and frequency of detection (population2)

0 - 20 percent 

urban

21 - 40 percent 

urban

41 - 60 percent 

urban

61 - 80 percent 

urban

81 - 100 percent 

urban

Any volatile organic 

compound

0.0323 24 (A) 29 (AB) 27 (AB) 33 (AB) 42 (B)

Trihalomethanes 0.8277 15 (A) 16 (A) 10 (A) 14 (A) 14 (A)

Non-trihalomethane 

compounds

<0.0001 11 (A) 17 (B) 19 (BC) 28 (BC) 34 (C)

Any gasoline compound 0.0749 8.3 (A) 11 (A) 12 (A) 19 (A) 14 (A)

Methyl tert-butyl ether 0.5055 7.9 (A) 9.0 (A) 9.9 (A) 12 (A) 14 (A)

BTEX3 compounds 0.0013 1.1(A) 2.5 (AB) 1.0 (AB) 8.8 (B) 2.0 (AB)

Solvents <0.0001 3.4 (A) 7.4 (B) 5.2 (AB) 16 (BC) 26 (C)

Refrigerants <0.0001 0.5 (A) 0.6 (A) 1.0 (AB) 0 (AB) 8.0 (B)

Fumigants 0.0912 0.2 (A) 0.6 (A) 2.1 (A) 0 (A) 2.0 (A)

Organic synthesis 

compounds

0.2317 0.7 (A) 0.6 (A) 0 (A) 3.5 (A) 2.0 (A)

Table 13. Statistical comparison of the occurrence of volatile organic compounds in source-water samples by population 

density

[Population density analyzed for four 1-km2 grid cells adjacent to the drinking-water source]

Volatile organic compound

or related compounds p-value1

1

p-value is the attained significance level; values shown in bold are significant at the 95-percent confidence level.

Population density and frequency

of detection (population2)

2

Population-density populations that share the same letter are not significantly different at the 95-percent confidence level.

Less than 1,000 people 

per square mile

Greater than 1,000 people 

per square mile

Any volatile organic compound 0.0003 24 (A) 38 (B)

Trihalomethanes 0.4921 14 (A) 16 (A)

Non-trihalomethane compounds <0.0001 13 (A) 28 (B)

Any gasoline compound 0.0001 8.2 (A) 19 (B)

Methyl tert-butyl ether <0.0001 7.0 (A) 17 (B)

BTEX3 compounds

3Benzene, toluene, ethylbenzene, and o-, m-, and p-xylenes.

0.2192 1.6 (A) 3.3 (A)

Solvents 0.0009 4.9 (A) 12 (B)

Refrigerants 0.0020 0.4 (A) 3.3 (B)

Fumigants 0.3837 0.3 (A) 1.1 (A)

Organic synthesis compounds 0.9268 0.8 (A) 1.1 (A)
44 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

The occurrence of MTBE in finished drinking 

water (Squillace and Moran, 2000; Grady and Casey, 

2001) and in ambient ground- and surface waters 

(Moran, Halde, and others, 1999; Moran, Zogorski, and 

others, 1999; Squillace and others, 1999; Moran and 

others, 2002) also has been previously shown to be 

associated with patterns of MTBE use. Areas of the 

country that participate in the Federal RFG Program 

(U.S. Environmental Protection Agency, 1999b) and 

(or) the winter OXY Program (U.S. Environmental 

Protection Agency, 1999c), and where MTBE is known 

to be currently or formerly the oxygenate used to meet 

program requirements, have been found by the above 

investigators to correlate with higher MTBE occurrence. Similarly, the distribution of source waters that 

have concentrations of MTBE equal to or greater than 

the MRL also is related to the distribution of high 

MTBE-use areas (fig. 22). A statistical comparison of 

the frequency of detection of MTBE and other gasoline-related VOCs for areas that have and have not used 

fuels containing elevated concentrations of MTBE is 

summarized in table 14. MTBE was detected in 

drinking-water sources five times more frequently in 

the high MTBE-use areas than in areas that have not 

had comparable MTBE use. Although a similar pattern 

was observed for the subgroup “any gasoline compound,” this is probably due to the fact that MTBE 

alone contributes two-thirds of all gasoline compound 

detections in source waters. BTEX compounds, which 

were comparatively rarely detected (1.9 percent) in 

source-water samples, were not statistically related to 

MTBE-use patterns. BTEX compounds, however, are 

intrinsic components of all types of gasoline and would 

not be expected to be statistically related to either high 

or low MTBE-use areas.

Lastly, the occurrence of gasoline-related VOCs 

in source water was compared to the density of chemical storage tanks, the great majority of which store 

gasoline, near the drinking-water source. Information 

on the locations of above- and below-ground storage 

tanks, as well as information on the number of leaking 

underground storage tanks, was obtained from StarView Real Estate Version 2.6.1 (Vista Information 

Solutions, 1999), and the density of these sites within 

the 4-km2

 grid surrounding source-water locations was 

calculated. Drinking-water sources were then characterized as having storage-tank densities of 0, greater 

than 0 to 1.0 (numerical average density), greater than 

1.0 to 5.0, greater than 5.0 to 10.0, or greater than 

10.0 tanks/mi2 in their vicinity, and the frequency of 

detection of gasoline compounds was tested for independence with respect to tank-density category. The 

results of this analysis (table 15) show that any gasoline 

compound, collectively, and BTEX compounds were 

detected significantly more often where there were 

more than 10 storage tanks per square mile. MTBE 

detections, conversely, were not related to storage-tank 

density at all. Although leaking underground storage 

tanks clearly have been sources of MTBE contamination of ground water (Happel and others, 1998; Hitzig 

and others, 1998), other studies have similarly reported 

the lack of a statistically significant association 

between MTBE detections in drinking-water wells and 

the proximity (State of Maine, 1998) or density 

(Shelton and others, 2001) of gasoline storage tanks. 

The lack of a statistically significant relation between 

MTBE detections and storage-tank density may reflect 

the enhanced mobility and recalcitrance of MTBE 

relative to most other gasoline compounds in ground 

water and (or) a greater variety of nonpoint sources 

such as small leaks and spills, urban runoff, recreational water-craft use, and atmospheric transport.

1

p-value is the attained significance level; values shown in bold are significant at the 95-percent confidence level.

2MTBE-use populations that share the same letter are not significantly different at the 95-percent confidence level. 3

Benzene, toluene, ethylbenzene, and o-xylene and, m-, p-xylene.

Table 14. Statistical comparison of the occurrence of methyl tert-butyl ether (MTBE) and other gasoline-related

volatile organic compounds in source-water samples by MTBE-use area

Volatile organic compound or 

related compounds p-value1

MTBE use and frequency of detection (population2)

Source waters not in high

MTBE-use area

Source waters in high

MTBE-use area

Any gasoline compound <0.0001 6.2 (A) 23 (B)

Methyl tert-butyl ether <0.0001 4.4 (A) 23 (B)

BTEX3 compounds 0.9485 2.0 (A) 1.8 (A)
Occurrence and Distribution of VOCs in Drinking-Water Sources 45 Figure 22. Distribution of methyl tert-butyl ether (MTBE) detections in ground- and surface-water sources in the United States and Puerto Rico in relation to high MTBE-use areas. AREAS WITH HIGH- VOLUME MTBE USE EXPLANATION MTBE not detected MTBE detected MTBE not detected MTBE detected GROUND-WATER SOURCE SURFACE-WATER SOURCE
46 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

1

p-value is the attained significance level; values shown in bold are significant at the 95-percent confidence level. 2

Storage-tank density populations that share the same letter are not significantly different at the 95-percent confidence level. 3

Benzene, toluene, ethylbenzene, and o-xylene, and m-, p-xylene.

Table 15. Statistical comparison of the occurrence of methyl tert-butyl ether (MTBE) and other gasoline-related 

volatile organic compounds in source-water samples by storage-tank density

[Storage tank density analyzed for four 1-km2 grid cells adjacent to the drinking-water source; mi2, square mile; >, greater than]

Volatile organic 

compound or 

related 

compound

p-value1

Storage-tank density and frequency of detection (population2)

0 tanks/mi2 >0 to 1.0 

tanks/mi2

>1.0 to 5.0 

tanks/mi2

>5.0 to 10.0 

tanks/mi2

>10.0

tanks/mi2

Any gasoline

 compound

0.0356 8.7 (A) 7.3 (A) 12 (AB) 15 (AB) 20 (B)

MTBE 0.4271 8.4 (A) 7.0 (A) 9.8 (A) 13 (A) 14 (A)

BTEX3 0.0192 1.3 (AB) 0.4 (A) 2.9 (AB) 3.6 (AB) 6.8 (B)

In summary, the occurrence of several subgroups 

of VOCs were shown to be statistically related to certain anthropogenic factors. The frequency of detection 

of any VOC, non-THM VOC, solvent, and refrigerant 

was significantly greater in some areas where the percentage of urban land use exceeded 20 percent and 

where population density exceeded 1,000 people/mi2. 

Although the frequency of detection of any gasolinerelated compound in general, and MTBE in particular, 

was not related to percentage of urban land use, the frequency of detection was greater in the high populationdensity areas and in areas with high-MTBE use as an 

oxygenate in gasoline. In particular, MTBE detections 

were five times more frequent in source waters in high 

MTBE-use areas than outside of these areas. Conversely, BTEX detections were greater in some more 

urbanized areas, but not directly related to population 

density or to high MTBE-use areas. Finally, the density 

of storage tanks around source waters affects the 

frequency of detection of gasoline-related VOCs in 

general, and BTEX in particular, but not MTBE.

SUMMARY AND CONCLUSIONS

The Random Survey was designed to provide 

representative information on the frequency of detection, concentration, distribution, and temporal variability of MTBE, other ether gasoline oxygenates, and 

other VOCs in source waters used by CWSs in the 

United States. The survey, sponsored by the American 

Water Works Association Research Foundation, was 

conducted by the U.S. Geological Survey in cooperation with Metropolitan Water District of Southern California and the Oregon Health & Science University. 

Source-water samples for the Random Survey 

were collected from 954 CWSs in the 50 States, Native 

American Lands, and Puerto Rico from May 3, 1999 to 

October 23, 2000. Samples were allocated proportionally to the total number of systems in each of the five 

population-served size categories, the total number of 

people served by each of the source-size category, and 

the type of source waters used. Untreated source-water 

samples from 579 ground-water sources (wells and 

springs) and 375 surface-water sources (rivers, lakes, 

and reservoirs) were collected by CWS personnel and 

sent to the MWDSC laboratory for analysis of MTBE, 

3 other ether gasoline oxygenates, and 62 additional 

VOCs. One source-water sample was collected and 

analyzed from each participating CWS.

Forty-two of the 66 VOC analytes were detected 

in at least one sample at concentrations equal to or 

greater than the MRL of 0.2 μg/L (for all VOCs except 

methyl ethyl ketone, which has an MRL of 2.0 μg/L). 

One or more VOCs were detected in 257 (27 percent) 

of the 954 source-water samples. Chloroform was the 

most frequently detected VOC in 13 percent of the samples; MTBE was second, detected in 8.7 percent of the 

samples. Although VOC detections were frequent, concentrations were generally less than 10 μg/L—

95 percent of all 530 VOC detections—and 63 percent 

were less than 1.0 μg/L. However, eight source-water 

samples contained one or more VOCs at concentrations 

that would have exceeded Federal maximum contaminant levels (MCLs) established for drinking water. 

When VOCs were detected in source-water samples, 

co-occurrence of several VOCs was fairly common, 
References Cited 47

with multiple detections in nearly half (47 percent) the 

257 samples with VOC detections.

Proportionally, more surface-water samples 

(30 percent) than ground-water samples (25 percent) 

contained VOCs. Gasoline compounds collectively and 

MTBE were detected significantly more often in 

surface-water sources than ground-water sources at the 

95-percent confidence level, whereas, the opposite was 

true of solvents and refrigerants. For most VOC subgroups, detections were more frequent in samples from 

the largest water systems as their source waters are 

more likely to be in urban settings. Detection frequencies for any VOC, non-THM VOCs, BTEX compounds, solvents, and refrigerants were significantly 

greater in source-water samples from areas with 60 percent or more urban land use than in less urbanized 

areas. Also, drinking-water sources in areas with population density greater than 1,000 people per square mile 

contained any VOC, non-THM VOCs, gasoline compounds collectively, MTBE, solvents, and refrigerants 

significantly more often than source waters in less 

densely populated settings.

The widespread occurrence of THM disinfectant 

by-products in source waters probably represents the 

persistence of residual concentrations of disinfectant 

by-products from chlorinated drinking water and 

wastewater circulating through the hydrologic cycle. 

The more frequent detections of MTBE in surfacewater sources (14 percent) than ground-water sources 

(5.4 percent) probably is related to emissions and leaks 

or spills of gasoline from personal and commercial 

motorized watercraft operated on surface-water bodies 

that are used for drinking-water supply. Detections of 

MTBE in surface-water samples were most frequent in 

samples collected during summer months, reflecting 

the seasonal use of watercraft, whereas detections in 

ground water did not demonstrate any seasonal effects. 

Concentrations of MTBE in source-water samples were 

generally less than 5.0 μg/L, however, and only one 

sample approached the 20-μg/L lower level of the 

Federal recommended drinking-water advisory. Cooccurrence of MTBE and BTEX was limited to a few 

samples with low concentrations of both gasoline 

contaminants. Detections of other ether gasoline 

oxygenates—ethyl tert-butyl ether, tert-amyl methyl 

ether, and diisopropyl ether—were rare and only 

occurred with MTBE.

The frequency of detecting MTBE in sourcewater samples was significantly greater in source 

waters located in areas of the Nation where MTBE is 

used in high volume in gasoline (23 percent) compared 

to drinking-water sources outside of these areas 

(4.4 percent). This five-fold increase in MTBE detections in high MTBE-use areas is consistent with observations made in two previous studies—a national 

study of MTBE occurrence in ambient ground water 

and a regional study for the Northeast and MidAtlantic regions in drinking water. Although detections of gasoline compounds collectively and BTEX 

compounds were greater in source-water samples 

from areas with 10 or more gasoline storage tanks, 

MTBE detections were not significantly related to the 

density of gasoline storage tanks near the source 

waters. Similar observations regarding the lack of an 

association between MTBE detections in drinking 

water and storage-tank density and (or) proximity 

were made by previous investigations in California 

and Maine. This observation reflects the enhanced 

mobility and recalcitrance of MTBE relative to other 

gasoline contaminants and points to a greater variety 

of potential nonpoint MTBE sources such as small 

leaks and spills, urban runoff, recreational watercraft 

use, and atmospheric transport.

REFERENCES CITED

Arizona Department of Environmental Quality, 1999, 

Report on methyl tertiary butyl ether (MTBE), 

October 1, 1999: Arizona Dept. of Environmental 

Quality, accessed March 1, 2002, at 

http://www.adeq.state.az.us/environ/waste/ust/ 

mtbe.html.

Baehr, A.L., Stackelberg, P.E., and Baker, R.J., 1999, Evaluation of the atmosphere as a source of volatile organic 

compounds in shallow groundwater: Water Resources 

Research, v. 35, no. 1, p. 127-136.

Bender, D.A., Zogorski, J.S., Luo, Wentai, Pankow, J.F., 

Majewski, M.S., and Baker, R.J., 2000, Atmosphericwater interaction of chloroform, toluene, and MTBE in 

small perennial urban streams, in Air and Waste Management Association Conference and Exposition, 

93rd, Salt Lake City, Utah, June 18-22, 2000 [Proceedings]: Sewickley, Penn., Air and Waste Management 

Association Paper 706, 11 p. [CD-ROM].

Boughton, C.J., and Lico, M.S., 1998, Volatile organic 

compounds in Lake Tahoe, Nevada and California, 

July-September 1997: U.S. Geological Survey Fact 

Sheet FS-055-98, 2 p.

Bourelle, Andy, 1998, MTBE—A real concern for South 

Lake Tahoe: Tahoe Daily Tribune, August 28, 1998, 

accessed December 6, 2000, at URL 

http://www.tahoe.com/tribune/ stories.8.28.98/ 

news/mt28Aug1347.html.
48 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Bush, P.W., Ardis, A.F., Fahlquist, Lynne, Ging, P.B., 

Horning, C.E., and Lanning-Rush, Jennifer, 2000, 

Water quality in south-central Texas, 1996-98: U.S. 

Geological Survey Circular 1212, 32 p.

California Department of Health Services, 2001, MTBE in 

California drinking water: accessed December 6, 2000, 

at URL http://www.dhs.cahwnet.gov/ps/ddwem/

chemicals/ mtbe/mtbeindex.htm.

California Environmental Protection Agency, 1997, MTBE 

(methyl tertiary butyl ether), Briefing paper prepared by 

the California Environmental Protection Agency, 

April 24, 1997 (updated September 3, 1998), accessed 

February 28, 2002, at 

http://www.arb.ca.gov/cbg/oxy/oxy.htm.

California Senate, 1998, Does California need MTBE? prepared by Kip Wiley, February 1998, accessed February 

28, 2002, at http://www.sen.ca.gov/ftp/sen/sor/

environ/98mtbe.htm.

City of Santa Monica, 1999, MTBE issue featured on “60 

Minutes”: accessed December 6, 2000, at URL 

http://epwm.santamonica.org/epwm/watquality/

1999report/waterweb/news05.htm.

Dale, M.S., Koch, Bart, Losee, R.F., Crofts, E.W., and Davis, 

M.K., 2000, MTBE in Southern California 

water—Motorized recreation watercraft were the predominant mode of contamination in reservoirs: Journal 

American Water Works Association, v. 92, no. 8,

p. 42-51.

Delzer, G.C., 2002, A review of literature for methyl tertbutyl ether in sources of drinking water in the United 

States: U.S. Geological Survey Open-File Report 

01-322, 16 p.

Delzer, G.C., Zogorski, J.S., Lopes, T.J., and Bosshart, R.L., 

1996, Occurrence of the gasoline oxygenate MTBE and 

BTEX compounds in urban stormwater in the United 

States, 1991-95: U.S. Geological Survey WaterResources Investigations Report 96-4145, 6 p.

Gabele, P.A., and Pyle, S.M., 2000, Emissions from two outboard engines operating on reformulated gasoline containing MTBE: Environmental Science & Technology, 

v. 34, no. 3, p. 368-372.

Gomez, Jose, Brasil, Tony, and Chan, Nelson, 1998, An 

overview of the use of oxygenates in gasoline: 

California Environmental Protection, Air Resource 

Board, 31 p.

Grady, S.J., 1994, Effects of land use on quality of water in 

stratified-drift aquifers in Connecticut—Chapter B, 

Analysis of nonpoint-source ground-water contamination in relation to land use: U.S. Geological Survey 

Water-Supply Paper 2381, 56 p.

Grady, S.J., and Casey, G.D., 2001, Occurrence and distribution of methyl tert-butyl ether and other volatile organic 

compounds in drinking water in the Northeast and MidAtlantic regions of the United States, 1993-98: U.S. 

Geological Survey Water-Resources Investigations 

Report 00-4228, 123 p.

Grady, S.J., and Mullaney, J.R., 1998, Natural and human 

factors affecting shallow water quality in surficial 

aquifers in the Connecticut, Housatonic, and Thames 

River Basins: U.S. Geological Water-Resources Investigations Report 98-4042, 81 p.

Happel, A.M., Dooher, B., Beckenbach, E.H., 1998, Methyl 

tertiary butyl ether (MTBE) impacts to California 

groundwater: Livermore, Calif., Lawrence Livermore 

National Laboratory, URCL-AR-130897, 68 p.

Hatten, Greg, 2000, MTBE treatment systems in Kansas: 

Association of State and Territorial Solid Waste 

Management Officials, MTBE and Fuel Oxygenates 

Workgroup Newsletter, v. 3, no. 1, 31 p.

Helsel, D.R., and Hirsch, R.M., 1992, Statistical methods in 

water resources: New York, Elsevier Science, 522 p.

Hitzig, R., Kostecki, P., and Leonard, D., 1998, Study reports 

LUST programs are feeling effects of MTBE releases: 

Soil & Groundwater Cleanup, Aug/Sept. 1998, 

p. 15-19.

Hunter, Bruce, 1999, Impacts of small gasoline spills on 

groundwater [abs.], in MTBE & other toxics in Maine’s 

environment, 1999 Maine Water Conference, presentation, April 15, 1999: Augusta, Maine, Maine Department of Environmental Protection.

Iman, R.L., and Conover, W.J., 1983, A modern approach to 

statistics: New York, John Wiley and Sons, 497 p.

Ivahnenko, T.I., Grady, S.J., and Delzer, G.C., 2001, Design 

of a national survey of methyl tert-butyl ether and other 

volatile organic compounds in drinking-water sources: 

U.S. Geological Survey Open-File Report 01-271, 42 p.

Juttner, Friedrich, Backhaus, Diedrich, Matthias, Uwe, 

Essers, Ulf, Greiner, Rolf, and Mahr, Bernd, 1995, 

Emissions of two- and four-stroke outboard engines, 

I. Quantification of gases and VOC: Water Research, 

v. 29, no. 8, p. 1976-1982.

Lopes, T.J., and Bender, D.A., 1998, Nonpoint sources of 

volatile organic compounds in urban areas—Relative 

importance of land surfaces and air: Environmental Pollution, v. 101, p. 221-230. 

Minear, R.A., and Amy, G.L., (eds.), 1995, Disinfection byproducts in water treatment—The chemistry of their 

formation and control: New York, Lewis Publishers, 

520 p.

Moran, M.J., Clawges, R.M., and Zogorski, J.S., 2002, 

Methyl tert-butyl ether in ground and surface water of 

the United States, in Diaz, A.L., and Drogos, D.L., 

(eds.), Oxygenates in gasoline—Environmental 

aspects: Washington, D.C., American Chemical Society 

Symposium Series 799, p. 2-16.

Moran, M.J., Halde, M.J., Clawges, R.M., and Zogorski, 

J.S., 1999, Relations between the detection of methyl 

tert-butyl ether (MTBE) in surface and ground water 

and its content in gasoline, in the American Chemical 

Society preprints of papers, 219th, San Francisco, 

Calif., Mar. 26-31, 2000: Cape Girardeau, Mo., 

American Chemical Society, v. 40, no.1, p. 195-198.
References Cited 49

Moran, M.J., Zogorski, J.S., and Squillace, P.J., 1999, MTBE 

in ground water of the United States—Occurrence, 

potential sources, and long-range transport, in Water 

Resources Conference, American Water Works Association, Sept. 26-29, 1999, Norfolk, Va., [Proceedings]: 

Denver, Colo., American Water Works Association.

Pankow, J.F., Thomson, N.R., Johnson, R.L., Baehr, A.L., 

and Zogorski, J.S., 1997, The urban atmosphere as a 

non-point source for the transport of MTBE and other 

volatile organic compounds (VOCs) to shallow ground 

water: Environmental Science & Technology, v. 31, 

no. 10, p. 2821-2828.

Pomes, M.L., Green, W.R., Thurman, E.M., Orem, W.H., and 

Lerch, H.E., 1999, DBP formation potential of aquatic 

humic substances: Journal of the American Water 

Works Association, v. 91, no. 3, p. 101-115.

Price, C.V., and Clawges, R.M., 1999, Digital data sets 

describing water use, toxic chemical releases, metropolitan areas, and population density of the conterminous 

United States: U.S. Geological Survey Open-File 

Report 99-78, scale 1:2,000,000 [CD-ROM disk].

Reiser, R.G., and O’Brien, A.K., 1998, Occurrence and seasonal variability of volatile organic compounds in seven 

New Jersey streams: U.S. Geological Survey WaterResources Investigations Report 98-4074, 11 p. 

Reuter, J.E., Allen, B.C., Richards, R.C., Pankow, J.F., Goldman, C.R., Sholl, R.L., and Seyfried, J.S., 1998, Concentrations, sources, and fate of the gasoline oxygenate 

methyl tert-butyl ether (MTBE) in a multiple-use lake: 

Environmental Science & Technology, v. 32, no. 23, 

p. 3666-3672.

Robbins, G.A., Henebry, B.J., Schmitt, B.M., Bartolomeo, 

F.B., Green, A., and Zack, P., 1999, Evidence for MTBE 

in heating oil: Ground Water Monitoring Review, v. 19, 

no. 2, p. 65-69.

Shelton, J.L., Burrow, K.R., Belitz, Kenneth, Dubrovsky, 

N.M., Land, Michael, and Gronberg, JoAnn, 2001, 

Low-level volatile organic compounds in active public 

supply wells as ground-water tracers in the Los Angeles 

physiographic basin, California, 2000: U.S. Geological 

Survey Water-Resources Investigations Report 

01-4188, 29 p.

Solley, W.B., Pierce, R.R., and Perlman, H.A., 1998, Estimated use of water in the United States in 1995:

U.S. Geological Survey Circular 1200, 71 p.

Squillace, P.J., and Moran, M.J., 2000, Estimating the likelihood of MTBE occurrence in drinking water supplied 

by ground-water sources in the Northeast and MidAtlantic regions of the United States: U.S. Geological 

Survey Open-File Report 00-343, 10 p.

Squillace, P.J., Moran, M.J., Lapham, W.W., Price, C.V., 

Clawges, R.M., and Zogorski, J.S., 1999, Volatile 

organic compounds in untreated ambient groundwater 

of the United States, 1985-1995: Environmental 

Science & Technology, v. 33, no. 23, p. 4176-4187.

State of Maine, 1998, The presence of MTBE and other gasoline compounds in Maine’s drinking water, preliminary report, October 13: State of Maine, Bureau of 

Health, Bureau of Waste Management and Redmediation, Maine Geological Survey, Augusta, Maine, 23 p.

U.S. Environmental Protection Agency, 1995, Methods for 

the determination of organic compounds in drinking 

water—Supplement III: U.S. Environmental Protection Agency, Office of Research and Development, 

Cincinnati, Ohio, EPA-600/R-95-131.

———1997a, Drinking Water Advisory—Consumer 

acceptability advice and health effects analysis on 

methyl tertiary-butyl ether (MTBE): U.S. Environmental Protection Agency, Office of Water, EPA-822-

F-97-009, 4 p.

———1997b, The national public water system supervision program—FY 1996 compliance report: U.S. 

Environmental Protection Agency, Office of Enforcement and Compliance Assurance, 45 p.

———1998a, Announcement of the drinking water contaminant candidate list, notice (March 12, 1998): 

Federal Register, v. 63, no. 40, p. 10273-10287.

———1998b, Safe drinking water information system: 

accessed at URL 

http://www.epa.gov/enviro/html/sdwis/.

———1999a, Revisions to the unregulated contaminant 

monitoring regulation for public water systems; Final 

rule (September 17, 1999): Federal Register, v. 64, 

no. 180, p. 50556-50620.

———1999b, List of reformulated gasoline program areas: 

Office of Mobile Sources, accessed April 5, 1999, at 

URL http://www.epa.gov/oms/rfgarea.htm.

———1999c, Winter oxygenated fuels program: Office of 

Mobile Sources, accessed June 16, 1999, at URL 

http://www.epa.gov/oms/fuels.htm.

———2000, Drinking water standards and health advisories: U.S. Environmental Protection Agency, Office of 

Water, EPA 822-B-00-001, 17 p.

Vista Information Solutions, 1999, StarView Real Estate 

Version 2.6.1, Users Guide: San Diego, Calif., Vista 

Information Solutions, 228 p.

Vogelmann, J.E., Howard, S.M., Yang, L., Larson, C.R., 

Wylie, B.K., and Van Driel, J.N., 2001, Completion of 

the 1990’s National Land Cover Data Set for the conterminous United States: Photogrammetric Engineering and Remote Sensing, v. 67, p. 650-662. 

Westrick, J.J., 1990, National surveys of volatile organic 

compounds in ground and surface waters, in Ram, 

N.M., Christman, R.F., and Cantor, K.P., eds., Significance and treatment of volatile organic compounds in 

water supplies: Chelsea, Mich., Lewis Publishers, Inc., 

p. 103-125.
50 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Zapecza, O.S., and Baehr, A.L., 1999, Methyl tert-butyl 

ether (MTBE) in lakes in Byram Township, Sussex 

County, New Jersey, 1998, and implications for ground 

water vulnerability, in Morganwalp, D.W., and Buxton, 

H.T., (eds.), U.S. Geological Survey Toxics Hydrology 

Program—Proceedings of the Technical Meeting, 

Volume 2, Contamination of Hydrologic Systems and 

Related Ecosystems, Charleston, S.C., March 8-12, 

1999 [Proceedings]: U.S. Geological Survey WaterResources Investigations Report 99-4018B, p. 405-414.

Zogorski, J.S., Morduchowitz, A.M., Baehr, A.L., Bauman, 

B.J., Conrad, D.L., Drew, R.T., Korte, N.E., Lapham, 

W.W., Pankow, J.F., and Washington, E.R., 1997, Fuel 

oxygenates and water quality, chapter 2 of the Interagency Assessment of Oxygenated Fuels: Washington, 

D.C., National Science and Technology Council, Office 

of Science and Technology Policy, p. 2-1 to 2-80.
APPENDIXES
52 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey [Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than] Question Source-water type and size of community water system TOTAL Ground water Rivers Reservoirs VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL 1. What type of source water was sampled for this study? ground water 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575 surface water -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366 total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 941 2. How often do you monitor volatile organic compounds in the drinking-water source being sampled for this study? >once per month 0 1 0 1 3 5 0 0 0 0 7 7 0 0 0 1 2 3 15 monthly 29 5 4 3 8 49 1 0 1 4 2 8 0 0 0 0 6 6 63 quarterly 32 17 8 12 11 80 0 1 4 7 25 37 1 4 6 15 32 58 175 annual 44 23 5 10 10 92 4 8 6 13 26 57 0 2 5 13 58 78 227 every 2 years 6 1 0 0 1 8 0 0 0 0 1 1 0 0 0 0 0 0 9 every 3 years 52 21 7 11 5 96 1 0 0 2 4 7 2 1 0 2 4 9 112 <every 3 years 3 0 4 3 1 11 1 1 0 1 1 4 0 0 0 0 2 2 17 as required 2 1 1 0 0 4 0 0 0 0 1 1 0 0 0 0 2 2 7 other 113 48 20 20 14 215 0 3 4 9 15 31 1 3 4 7 21 36 282 did not answer 10 3 0 2 0 15 0 1 0 3 6 10 0 0 0 1 8 9 34 total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 941 3. Do you monitor source water, finished water, or both? source water 115 50 16 17 15 213 2 0 3 2 5 12 3 0 1 5 11 20 245 finished water 85 31 14 18 13 161 4 6 6 25 42 83 1 6 9 25 55 96 340 both 79 34 19 26 24 182 1 8 5 12 40 66 0 4 5 9 63 81 329 did not answer 12 5 0 1 1 19 0 0 1 0 1 2 0 0 0 0 6 6 27 total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 941 4. Has methyl tert-butyl ether been detected in source-water samples from this drinking-water source within the last three years? yes 2 1 4 2 3 12 1 0 0 1 7 9 0 0 0 0 9 9 30 no 193 82 33 47 43 398 3 6 8 15 46 78 3 4 8 14 73 102 578

uncertain 76 31 8 11 3 129 2 8 4 17 26 57 1 5 4 19 37 66 252did not answer 20 6 4 2 4 36 1 0 3 6 9 19 0 1 3 6 16 26 81total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 941
Appendix 1 53

5. Has methyl tert-butyl ether been detected in finished-water samples from this drinking-water source within the last three years?yes 3 0 2 2 4 11 0 0 0 0 5 5 0 1 0 1 10 12 28no 172 64 31 45 38 350 6 7 10 28 54 105 3 4 11 23 85 126 581uncertain 63 32 12 6 4 117 1 6 3 10 19 39 1 4 4 14 29 52 208did not answer 53 24 4 9 7 97 0 1 2 1 10 14 0 1 0 1 11 13 124total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 9416. Have other volatile organic compounds (excluding trihalomethanes and other disinfectant by-products) been detected in source-water samples from this drinking-water 

source within the last three years?

yes 11 10 5 10 12 48 0 1 1 8 14 24 0 0 1 1 4 6 78no 200 72 35 45 35 387 3 7 6 14 41 71 3 4 7 23 84 121 579uncertain 60 28 6 4 2 100 1 6 4 12 22 45 1 3 3 7 26 40 185did not answer 20 10 3 3 4 40 3 0 4 5 11 23 0 3 4 8 21 36 99total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 941 7. Have other volatile organic compounds (excluding trihalomethanes and other disinfectant by-products) been detected in finished-water samples from this source within 

the last three years?

yes 17 5 4 5 13 44 1 2 2 8 18 31 0 3 4 8 18 33 108no 170 62 32 45 32 341 4 10 9 26 61 110 2 5 9 26 98 140 591uncertain 55 26 9 6 1 97 1 1 2 4 5 13 1 1 1 4 8 15 125did not answer 49 27 4 6 7 93 1 1 2 1 4 9 1 1 1 1 11 15 117total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 9418. (Pertaining to fuel use) Is the source water in an ozone non-attainment area?yes 15 5 1 2 2 25 0 0 0 2 16 18 1 0 1 0 18 20 63no 98 29 12 26 23 188 5 5 6 13 23 52 0 4 4 12 43 63 303uncertain 174 83 35 33 28 353 2 9 9 23 47 90 3 6 10 26 70 115 558did not answer 4 3 1 1 0 9 0 0 0 1 2 3 0 0 0 1 4 5 17total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 9419. Is the source water in an area where use of reformulated gasoline is required?yes 15 5 6 6 12 44 0 1 0 5 25 31 0 0 0 7 42 49 124no 164 65 27 40 28 324 6 8 8 19 29 70 2 5 11 16 46 80 474uncertain 102 47 15 16 13 193 1 5 7 15 33 61 2 5 4 15 43 69 323did not answer 10 3 1 0 0 14 0 0 0 1 1 2 0 0 0 0 4 4 20total 291 120 49 62 53 575 7 14 15 40 88 164 4 10 15 38 135 202 941

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); 

MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
54 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey 10. What type of ground-water source was sampled for this study? well 284 115 46 60 53 558 -- -- -- -- -- -- -- -- -- -- -- -- 558 spring 6 3 3 1 0 13 -- -- -- -- -- -- -- -- -- -- -- -- 13 gallery 1 1 0 1 0 3 -- -- -- -- -- -- -- -- -- -- -- -- 3 did not answer 0 1 0 0 0 1 -- -- -- -- -- -- -- -- -- -- -- -- 1 total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575 11. If source is a well (or wells), what is the depth of the well(s) below land surface (feet)? 0 - 250 141 51 20 28 19 259 -- -- -- -- -- -- -- -- -- -- -- -- 259 251 - 500 82 33 15 12 9 151 -- -- -- -- -- -- -- -- -- -- -- -- 151 501 - 750 23 11 3 11 8 56 -- -- -- -- -- -- -- -- -- -- -- -- 56 751 - 1,000 12 4 3 4 5 28 -- -- -- -- -- -- -- -- -- -- -- -- 28 >1,000 8 13 3 5 7 36 -- -- -- -- -- -- -- -- -- -- -- -- 36 did not answer 25 8 5 2 5 45 -- -- -- -- -- -- -- -- -- -- -- -- 45 total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575 12. What is the depth of the intake for the well pump (feet)? 0 - 250 151 61 22 42 41 317 -- -- -- -- -- -- -- -- -- -- -- -- 317 251 - 500 32 17 6 5 3 63 -- -- -- -- -- -- -- -- -- -- -- -- 63 501 - 750 12 3 1 5 1 22 -- -- -- -- -- -- -- -- -- -- -- -- 22 751 - 1,000 1 1 1 1 0 4 -- -- -- -- -- -- -- -- -- -- -- -- 4 >1,000 1 0 0 0 1 2 -- -- -- -- -- -- -- -- -- -- -- -- 2 did not answer 94 38 19 9 7 167 -- -- -- -- -- -- -- -- -- -- -- -- 167 total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575 13. What is the depth to the water level under static conditions (feet)? 0 - 200 164 76 33 49 41 363 -- -- -- -- -- -- -- -- -- -- -- -- 363 200 - 400 11 11 5 6 3 36 -- -- -- -- -- -- -- -- -- -- -- -- 36

>400 6 4 2 0 0 12 -- -- -- -- -- -- -- -- -- -- -- -- 12did not answer 110 29 9 7 9 164 -- -- -- -- -- -- -- -- -- -- -- -- 164total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
Appendix 1 55

14. What is the depth to the water level under pumping conditions (feet)?0 - 250 112 63 29 48 37 289 -- -- -- -- -- -- -- -- -- -- -- -- 289251 - 500 8 7 3 6 2 26 -- -- -- -- -- -- -- -- -- -- -- -- 26501 - 750 3 2 2 0 0 7 -- -- -- -- -- -- -- -- -- -- -- -- 7751 - 1,000 1 0 0 0 0 1 -- -- -- -- -- -- -- -- -- -- -- -- 1did not answer 167 48 15 8 14 252 -- -- -- -- -- -- -- -- -- -- -- -- 252total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 57515. What is the average volume pumped per day (gallons)?0 - 50,000 208 23 7 5 5 248 -- -- -- -- -- -- -- -- -- -- -- -- 24850,001 - 100,000 19 26 3 1 0 49 -- -- -- -- -- -- -- -- -- -- -- -- 49>100,000 21 66 34 56 46 223 -- -- -- -- -- -- -- -- -- -- -- -- 223did not answer 43 5 5 0 2 55 -- -- -- -- -- -- -- -- -- -- -- -- 55total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 57516. (Pertaining to well construction) How is the well finished?screened 160 80 35 49 37 361 -- -- -- -- -- -- -- -- -- -- -- -- 361open hole 40 16 5 7 14 82 -- -- -- -- -- -- -- -- -- -- -- -- 82uncertain 72 19 5 2 1 99 -- -- -- -- -- -- -- -- -- -- -- -- 99did not answer 19 5 4 4 1 33 -- -- -- -- -- -- -- -- -- -- -- -- 33total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 57517. What is the length of screened or open interval (feet)?0 - 50 60 31 12 18 13 134 -- -- -- -- -- -- -- -- -- -- -- -- 13451 - 100 3 5 6 5 9 28 -- -- -- -- -- -- -- -- -- -- -- -- 28101 - 150 1 3 0 2 1 7 -- -- -- -- -- -- -- -- -- -- -- -- 7151 - 200 4 2 1 4 1 12 -- -- -- -- -- -- -- -- -- -- -- -- 12201 - 250 2 1 0 0 1 4 -- -- -- -- -- -- -- -- -- -- -- -- 4>250 4 1 0 2 5 12 -- -- -- -- -- -- -- -- -- -- -- -- 12unknown 8 2 0 0 0 10 -- -- -- -- -- -- -- -- -- -- -- -- 10did not answer 209 75 30 31 23 368 -- -- -- -- -- -- -- -- -- -- -- -- 368total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); 

MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
56 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey 18. Is the aquifer lithology (composition) consolidated (for example, bedrock)? yes 92 29 10 13 12 156 -- -- -- -- -- -- -- -- -- -- -- -- 156 no 35 14 9 12 17 87 -- -- -- -- -- -- -- -- -- -- -- -- 87 uncertain 77 28 10 7 7 129 -- -- -- -- -- -- -- -- -- -- -- -- 129 did not answer 87 49 20 30 17 203 -- -- -- -- -- -- -- -- -- -- -- -- 203 total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575 19. Is the aquifer lithology (composition) unconsolidated (for example, sand and gravel)? yes 113 61 27 42 33 276 -- -- -- -- -- -- -- -- -- -- -- -- 276 no 17 6 3 3 3 32 -- -- -- -- -- -- -- -- -- -- -- -- 32 uncertain 79 27 9 7 6 128 -- -- -- -- -- -- -- -- -- -- -- -- 128 did not answer 82 26 10 10 11 139 -- -- -- -- -- -- -- -- -- -- -- -- 139 total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575 20. Is the aquifer confined (artesian conditions)? yes 42 15 14 20 15 106 -- -- -- -- -- -- -- -- -- -- -- -- 106 no 54 16 8 12 14 104 -- -- -- -- -- -- -- -- -- -- -- -- 104 uncertain 72 27 3 6 5 113 -- -- -- -- -- -- -- -- -- -- -- -- 113 did not answer 123 62 24 24 19 252 -- -- -- -- -- -- -- -- -- -- -- -- 252 total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575 21. Is the aquifer unconfined (water-table conditions)? yes 151 74 28 37 34 324 -- -- -- -- -- -- -- -- -- -- -- -- 324 no 6 3 2 5 5 21 -- -- -- -- -- -- -- -- -- -- -- -- 21 uncertain 76 23 4 4 4 111 -- -- -- -- -- -- -- -- -- -- -- -- 111 did not answer 58 20 15 16 10 119 -- -- -- -- -- -- -- -- -- -- -- -- 119 total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575 22. Is this source perceived or known to be under the influence of surface water?

yes 14 14 3 6 2 39 -- -- -- -- -- -- -- -- -- -- -- -- 39no 215 79 40 51 45 430 -- -- -- -- -- -- -- -- -- -- -- -- 430uncertain 59 21 6 5 5 96 -- -- -- -- -- -- -- -- -- -- -- -- 96did not answer 3 6 0 0 1 10 -- -- -- -- -- -- -- -- -- -- -- -- 10total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
Appendix 1 57

23. What is the distance to the nearest surface-water body (miles)?<1 135 44 22 31 17 249 -- -- -- -- -- -- -- -- -- -- -- -- 2491 - 25 91 49 21 20 28 209 -- -- -- -- -- -- -- -- -- -- -- -- 20926 - 50 7 4 2 1 0 14 -- -- -- -- -- -- -- -- -- -- -- -- 1451 - 75 0 1 0 1 0 2 -- -- -- -- -- -- -- -- -- -- -- -- 276 - 100 1 0 0 0 0 1 -- -- -- -- -- -- -- -- -- -- -- -- 1did not answer 57 22 4 9 8 100 -- -- -- -- -- -- -- -- -- -- -- -- 100total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 57524. Are there any petroleum refineries, pipelines, gas stations, or chemical underground storage tanks within 1/4-mile of the sampled source?yes 44 29 16 16 18 123 0 2 2 6 17 27 0 2 0 3 22 27 177no 225 84 29 43 28 409 6 11 13 30 54 114 4 7 14 35 102 162 685uncertain 19 6 4 3 6 38 1 1 0 3 15 20 0 1 1 1 5 8 66did not answer 3 1 0 0 1 5 0 0 0 0 2 2 0 0 0 0 6 6 13total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 94125. Are there any known contaminant sources in proximity to the sampled source that may impact chemical quality of the sampled source?yes 36 24 15 17 19 111 0 3 1 4 15 23 0 1 1 2 19 23 157no 224 81 25 42 28 400 6 4 13 30 57 110 4 8 14 36 105 167 677uncertain 26 12 7 3 5 53 1 7 1 5 14 28 0 1 0 1 5 7 88did not answer 5 3 2 0 1 11 0 0 0 0 2 2 0 0 0 0 6 6 19total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 94126. Are there any oil fields within 1/4-mile of the sampled source?yes 6 2 1 0 2 11 0 0 0 1 0 1 0 1 1 0 6 8 20no 265 107 45 57 47 521 6 12 12 33 80 143 4 9 14 37 114 178 842uncertain 16 10 3 5 3 37 1 2 3 5 6 17 0 0 0 2 14 16 70did not answer 4 1 0 0 1 6 0 0 0 0 2 2 0 0 0 0 1 1 9total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 94127. Has this well or any well within 1/4-mile of the well been closed within the past three years due to contamination by volatile organic compounds?yes 3 1 0 2 4 10 -- -- -- -- -- -- -- -- -- -- -- -- 10no 256 106 46 60 47 515 -- -- -- -- -- -- -- -- -- -- -- -- 515uncertain 29 10 1 0 1 41 -- -- -- -- -- -- -- -- -- -- -- -- 41did not answer 3 3 2 0 1 9 -- -- -- -- -- -- -- -- -- -- -- -- 9total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); 

MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
58 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey 28. Have there been any unusual storm events in the past two months? yes 17 9 4 7 6 43 2 3 2 2 13 22 2 2 1 4 24 33 98 no 250 105 43 45 41 484 2 11 13 30 58 114 2 8 9 30 90 139 737 did not answer 24 6 2 10 6 48 3 0 0 7 17 27 0 0 5 5 21 31 106 total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 941 29. Is there a watershed pollution prevention program at this source? yes -- -- -- -- -- -- 2 2 5 14 38 61 0 3 4 17 74 98 159 no -- -- -- -- -- -- 5 10 10 21 38 84 3 6 10 19 48 86 170 did not answer -- -- -- -- -- -- 0 2 0 4 12 18 1 1 1 3 13 19 37 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366 30. Is any fuel or chemical that might be a source of volatile organic compounds commercially transported on this water body within 1/4-mile of the intake of the sampled source? yes -- -- -- -- -- -- 0 1 0 7 18 26 1 0 1 2 20 24 50 no -- -- -- -- -- -- 7 11 14 30 55 117 3 10 12 34 97 156 273 uncertain -- -- -- -- -- -- 0 2 1 2 13 18 0 0 2 3 17 22 40 did not answer -- -- -- -- -- -- 0 0 0 0 2 2 0 0 0 0 1 1 3 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366 31. Are private motorized watercraft operated on this water body? yes -- -- -- -- -- -- 1 5 12 24 66 108 4 6 8 19 82 119 227 no -- -- -- -- -- -- 6 9 3 15 19 52 0 4 7 20 51 82 134 uncertain -- -- -- -- -- -- 0 0 0 0 0 0 0 0 0 0 0 0 0 did not answer -- -- -- -- -- -- 0 0 0 0 3 3 0 0 0 0 2 2 5 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366 32. Are official use, motorized watercraft operated on this water body? yes -- -- -- -- -- -- 1 5 3 17 54 80 4 4 7 21 115 151 231

no -- -- -- -- -- -- 6 9 12 21 29 77 0 6 8 18 17 49 126uncertain -- -- -- -- -- -- 0 0 0 1 1 2 0 0 0 0 0 0 2did not answer -- -- -- -- -- -- 0 0 0 0 4 4 0 0 0 0 3 3 7total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
Appendix 1 59

33. What is the estimated number of two-stroke motorized watercraft operated monthly on this water body?0 - 10 -- -- -- -- -- -- 3 5 7 3 8 26 0 2 1 7 15 25 5110 - 50 -- -- -- -- -- -- 0 0 0 2 8 10 0 0 2 3 12 17 27>100 -- -- -- -- -- -- 0 2 3 8 28 41 2 2 3 9 52 68 109did not answer -- -- -- -- -- -- 4 7 5 26 44 86 2 5 9 20 56 92 178total -- -- -- -- -- -- 7 14 15 39 88 163 4 9 15 39 135 202 36534. What is the estimated number of four-stroke motorized watercraft operated monthly on this water body?0 - 10 -- -- -- -- -- -- 3 3 3 3 11 23 0 1 1 7 9 18 4110 - 50 -- -- -- -- -- -- 0 0 0 3 9 12 0 0 2 3 10 15 27>100 -- -- -- -- -- -- 0 2 1 6 24 33 2 1 2 10 43 58 91did not answer -- -- -- -- -- -- 4 9 11 27 44 95 2 8 10 19 73 112 207total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 36635. What is the estimated number of personal motorized watercraft (jet skis) operated monthly on this water body?0 - 10 -- -- -- -- -- -- 3 3 2 3 9 20 0 1 2 5 17 25 4510 - 50 -- -- -- -- -- -- 0 0 0 1 10 11 0 0 2 3 6 11 22>100 -- -- -- -- -- -- 0 2 0 6 24 32 2 1 2 8 39 52 84did not answer -- -- -- -- -- -- 4 9 13 29 45 100 2 8 9 23 73 115 215total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 36636. Are there any horsepower restrictions on motorized watercraft used on this water body?yes -- -- -- -- -- -- 0 1 2 2 7 12 0 2 3 10 30 45 57no -- -- -- -- -- -- 3 8 12 30 64 117 4 4 6 17 79 110 227did not answer -- -- -- -- -- -- 4 5 1 7 17 34 0 4 6 12 26 48 82total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 36637. Are there any restrictions on the number of watercraft that can be operated on this water body?yes -- -- -- -- -- -- 0 1 1 1 7 10 0 0 1 11 36 48 58no -- -- -- -- -- -- 3 8 12 30 64 117 4 6 8 17 77 112 229did not answer -- -- -- -- -- -- 4 5 2 8 17 36 0 4 6 11 22 43 79total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); 

MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
60 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey 38. What is the distance from shoreline to the intake opening (feet)? <10 -- -- -- -- -- -- 4 3 4 16 45 72 0 2 0 6 19 27 99 10 - 100 -- -- -- -- -- -- 1 8 9 11 11 40 2 5 11 16 50 84 124 101 - 1,000 -- -- -- -- -- -- 0 2 0 3 9 14 2 3 1 6 31 43 57 >1,000 -- -- -- -- -- -- 0 0 1 1 3 5 0 0 1 4 21 26 31 did not answer -- -- -- -- -- -- 2 1 1 8 20 32 0 0 2 7 14 23 55 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366 39. What is the depth of intake below the water surface (feet)? <10 -- -- -- -- -- -- 4 7 7 19 44 81 1 8 7 4 15 35 0 10 - 100 -- -- -- -- -- -- 1 4 7 13 26 51 3 2 8 27 96 136 0 >100 -- -- -- -- -- -- 0 0 0 0 0 0 0 0 0 2 9 11 0 did not answer -- -- -- -- -- -- 2 3 1 7 18 31 0 0 0 6 15 21 0 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 0 40. What is the intake construction material? concrete -- -- -- -- -- -- 1 3 6 17 52 79 0 2 6 13 63 84 163 iron or steel -- -- -- -- -- -- 4 9 8 19 22 62 2 8 9 23 50 92 154 other material -- -- -- -- -- -- 1 0 0 1 4 6 2 0 0 0 16 18 24 did not answer -- -- -- -- -- -- 1 2 1 2 10 16 0 0 0 3 6 9 25 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366 41. How does water flow enter the intake? pumped -- -- -- -- -- -- 3 5 8 20 44 80 3 7 8 11 56 85 165 gravity flow -- -- -- -- -- -- 4 9 5 14 37 69 0 2 7 24 69 102 171 both -- -- -- -- -- -- 0 0 1 4 4 9 0 0 0 4 5 9 18 did not answer -- -- -- -- -- -- 0 0 1 1 3 5 1 1 0 0 5 7 12 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366

42. What is the distance from the intake to the sample-collection port (feet)?<1,000 -- -- -- -- -- -- 2 5 5 19 44 75 0 7 8 12 49 76 1511,000 - 10,000 -- -- -- -- -- -- 2 6 5 9 16 38 1 0 2 13 30 46 84>10,000 -- -- -- -- -- -- 0 1 3 4 4 12 0 1 3 7 23 34 46did not answer -- -- -- -- -- -- 3 2 2 7 24 38 3 2 2 7 33 47 85total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
Appendix 1 61

43. Is there a tiered tower at the intake to allow for withdrawals from selective depths?yes -- -- -- -- -- -- 0 2 1 3 8 14 0 2 7 18 67 94 108no -- -- -- -- -- -- 5 11 9 29 66 120 4 6 8 21 58 97 217did not answer -- -- -- -- -- -- 2 1 5 7 14 29 0 2 0 0 10 12 41total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 36644. What is the surface area of the lake or reservoir (acres)?<1,000 -- -- -- -- -- -- -- -- -- -- -- -- 0 8 8 23 50 89 891,000 - 10,000 -- -- -- -- -- -- -- -- -- -- -- -- 0 0 0 0 39 39 3910,000 - 100,000 -- -- -- -- -- -- -- -- -- -- -- -- 1 0 2 4 8 15 15>100,000 -- -- -- -- -- -- -- -- -- -- -- -- 1 1 0 3 15 20 20did not answer -- -- -- -- -- -- -- -- -- -- -- -- 2 1 5 9 23 40 40total -- -- -- -- -- -- -- -- -- -- -- -- 4 10 15 39 135 203 20345. What is the average depth of the lake or reservoir (feet)?<20 -- -- -- -- -- -- -- -- -- -- -- -- 0 6 6 11 26 49 020 - 100 -- -- -- -- -- -- -- -- -- -- -- -- 1 4 7 13 63 88 88>100 -- -- -- -- -- -- -- -- -- -- -- -- 1 0 0 4 17 22 22did not answer -- -- -- -- -- -- -- -- -- -- -- -- 2 0 2 11 29 44 44total -- -- -- -- -- -- -- -- -- -- -- -- 4 10 15 39 135 203 20346. What is the storage volume of the lake or reservoir (million gallons)?<1,000 -- -- -- -- -- -- -- -- -- -- -- -- 0 6 9 19 14 48 481,000 - 10,000 -- -- -- -- -- -- -- -- -- -- -- -- 1 0 1 5 42 49 4910,000 - 100,000 -- -- -- -- -- -- -- -- -- -- -- -- 0 0 1 1 38 40 40>100,000 -- -- -- -- -- -- -- -- -- -- -- -- 0 1 0 5 16 22 22did not answer -- -- -- -- -- -- -- -- -- -- -- -- 3 3 4 9 25 44 44total -- -- -- -- -- -- -- -- -- -- -- -- 4 10 15 39 135 203 20347. What is the average flow in the river (cubic feet per second)?<100 -- -- -- -- -- -- 0 4 6 12 8 30 -- -- -- -- -- -- 30100 - 1,000 -- -- -- -- -- -- 1 1 3 7 15 27 -- -- -- -- -- -- 27>1,000 -- -- -- -- -- -- 0 2 0 8 33 43 -- -- -- -- -- -- 43did not answer -- -- -- -- -- -- 6 7 6 12 32 63 -- -- -- -- -- -- 63total -- -- -- -- -- -- 7 14 15 39 88 163 -- -- -- -- -- -- 163

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); 

MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
62 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey 48. Does the lake or reservoir stratify during the year? yes -- -- -- -- -- -- -- -- -- -- -- -- 2 6 11 26 99 144 144 no -- -- -- -- -- -- -- -- -- -- -- -- 0 1 0 6 16 23 23 uncertain -- -- -- -- -- -- -- -- -- -- -- -- 2 2 4 4 11 23 23 did not answer -- -- -- -- -- -- -- -- -- -- -- -- 0 1 0 3 9 13 23 total -- -- -- -- -- -- -- -- -- -- -- -- 4 10 15 39 135 203 203 49. Does the source water body freeze over during the winter? yes -- -- -- -- -- -- -- -- -- -- -- -- 2 8 6 23 60 99 99 no -- -- -- -- -- -- -- -- -- -- -- -- 2 2 8 15 66 93 93 uncertain -- -- -- -- -- -- -- -- -- -- -- -- 0 0 0 0 0 0 0 did not answer -- -- -- -- -- -- -- -- -- -- -- -- 0 0 1 1 9 11 11 total -- -- -- -- -- -- -- -- -- -- -- -- 4 10 15 39 135 203 203 50. Is the source water disinfected prior to final distribution? yes 194 91 43 54 46 428 6 13 15 39 84 157 4 10 14 38 129 195 780 no 34 12 2 3 4 55 0 0 0 0 1 1 0 0 0 0 0 0 56 did not answer 63 17 4 5 3 92 1 1 0 0 3 5 0 0 1 1 6 8 105 total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 941 51. Is the source water aerated prior to final distribution? yes 15 18 15 24 19 91 -- -- -- -- -- -- -- -- -- -- -- -- 91 no 144 60 18 19 18 259 -- -- -- -- -- -- -- -- -- -- -- -- 259 did not answer 132 42 16 19 16 225 -- -- -- -- -- -- -- -- -- -- -- -- 225 total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575 52. Is the source water treated for iron and (or) manganese removal prior to final distribution? yes 37 25 13 25 10 110 -- -- -- -- -- -- -- -- -- -- -- -- 110

no 126 53 17 16 22 234 -- -- -- -- -- -- -- -- -- -- -- -- 234did not answer 128 42 19 21 21 231 -- -- -- -- -- -- -- -- -- -- -- -- 231total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 575

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
Appendix 1 63

53. Is the source water treated by oxidation prior to final distribution?yes 8 7 3 13 9 40 -- -- -- -- -- -- -- -- -- -- -- -- 40no 145 63 23 21 21 273 -- -- -- -- -- -- -- -- -- -- -- -- 273did not answer 138 50 23 28 23 262 -- -- -- -- -- -- -- -- -- -- -- -- 262total 291 120 49 62 53 575 -- -- -- -- -- -- -- -- -- -- -- -- 57554. Is the source water treated by conventional filtration prior to final distribution?yes -- -- -- -- -- -- 3 11 13 37 77 141 2 7 11 30 111 161 302no -- -- -- -- -- -- 2 2 1 1 7 13 1 1 1 2 15 20 33did not answer -- -- -- -- -- -- 2 1 1 1 4 9 1 2 3 7 9 22 31total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 36655. Is the source water treated by direct filtration prior to final distribution?yes -- -- -- -- -- -- 1 3 1 1 4 10 0 0 0 5 16 21 31no -- -- -- -- -- -- 3 4 3 13 38 61 2 1 4 15 56 78 139did not answer -- -- -- -- -- -- 3 7 11 25 46 92 2 9 11 19 63 104 196total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 36656. Is the source water treated by in-line filtration prior to final distribution?yes -- -- -- -- -- -- 2 0 1 1 1 5 2 1 0 1 4 8 13no -- -- -- -- -- -- 2 6 3 13 38 62 1 0 5 18 63 87 149did not answer -- -- -- -- -- -- 3 8 11 25 49 96 1 9 10 20 68 108 204total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 36657. Is the source water treated by slow sand filtration prior to final distribution? yes -- -- -- -- -- -- 4 2 2 4 6 18 1 3 5 1 7 17 35no -- -- -- -- -- -- 2 5 4 12 36 59 1 1 2 16 62 82 141did not answer -- -- -- -- -- -- 1 7 9 23 46 86 2 6 8 22 66 104 190total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 36658. Is the source water treated by softening prior to final distribution?yes -- -- -- -- -- -- 0 0 0 4 9 13 1 2 2 3 10 18 31no -- -- -- -- -- -- 4 7 4 13 35 63 2 1 5 17 62 87 150did not answer -- -- -- -- -- -- 3 7 11 22 44 87 1 7 8 19 63 98 185total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); 

MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
64 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey 59. Is the source water treated by two-stage softening prior to final distribution? yes -- -- -- -- -- -- 0 0 0 0 3 3 0 0 0 0 0 0 3 no -- -- -- -- -- -- 4 7 4 14 40 69 2 1 5 19 68 95 164 did not answer -- -- -- -- -- -- 3 7 11 25 45 91 2 8 10 20 67 108 199 total -- -- -- -- -- -- 7 14 15 39 88 163 4 9 15 39 135 203 366 60. Is the source water treated by coagulation and (or) sedimentation softening prior to final distribution? yes -- -- -- -- -- -- 1 6 11 28 49 95 2 9 13 23 69 116 211 no -- -- -- -- -- -- 3 5 1 5 14 28 1 0 0 5 35 41 69 did not answer -- -- -- -- -- -- 3 3 3 6 25 40 1 1 2 11 31 46 86 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366 61. Is the source water treated by split-treatment-softening prior to final distribution? yes -- -- -- -- -- -- 0 0 0 1 3 4 0 0 0 0 1 1 5 no -- -- -- -- -- -- 4 7 4 13 40 68 2 1 5 18 68 94 162 did not answer -- -- -- -- -- -- 3 7 11 25 45 91 2 9 10 21 66 108 199 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366 62. Is the source water treated by complex-parallel-train softening prior to final distribution? yes -- -- -- -- -- -- 0 0 0 1 1 2 0 0 0 0 0 0 2 no -- -- -- -- -- -- 4 7 4 13 41 69 2 1 5 18 68 94 163 did not answer -- -- -- -- -- -- 3 7 11 25 46 92 2 9 10 21 67 109 201 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366 63. Does the source water receive no treatment prior to final distribution? yes -- -- -- -- -- -- 0 0 0 0 1 1 0 0 0 0 4 4 5 no -- -- -- -- -- -- 4 5 3 14 38 64 2 1 3 23 56 85 149 did not answer -- -- -- -- -- -- 3 9 12 25 49 98 2 9 12 16 75 114 212 total -- -- -- -- -- -- 7 14 15 39 88 163 4 10 15 39 135 203 366

64. Are there any other treatment process used on the source water prior to final distribution?yes 57 29 21 24 30 161 0 1 2 7 13 23 0 0 0 7 34 41 225no 97 37 11 14 12 171 3 5 0 5 16 29 1 0 3 8 27 39 239did not answer 137 54 17 24 11 243 4 8 13 27 59 111 3 10 12 24 74 123 477total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 941

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
Appendix 1 65

65. Is the source water treated by granular activated carbon to remove volatile or other organic compounds?yes 1 2 2 0 6 11 1 0 0 2 22 25 0 2 1 2 15 20 56no 11 3 5 1 2 22 2 2 0 2 8 14 0 0 0 6 20 26 62did not answer 279 115 42 61 45 542 4 12 15 35 58 124 4 8 14 31 100 157 823total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 94166. Is the source water treated by powdered activated carbon to remove volatile or other organic compounds?yes 1 0 0 0 0 1 0 5 7 13 43 68 0 3 7 14 53 77 146no 11 3 5 1 2 22 4 5 2 9 19 39 2 1 2 9 37 51 112did not answer 279 117 44 61 51 552 3 4 6 17 26 56 2 6 6 16 45 75 683total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 94167. Is the source water treated with a membrane to remove volatile or other organic compounds?yes 1 0 0 0 1 2 1 0 0 1 0 2 0 0 0 0 5 5 9no 10 3 5 1 2 21 3 6 4 13 42 68 2 1 4 18 65 90 179did not answer 280 117 44 61 50 552 3 8 11 25 46 93 2 9 11 21 65 108 753total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 94168. Is the source water treated with ozone to remove volatile or other organic compounds?yes 0 0 0 0 1 1 0 0 0 0 3 3 0 0 0 0 11 11 15no 11 3 5 1 2 22 2 2 0 2 11 17 0 0 0 7 19 26 65did not answer 280 117 44 61 50 552 5 12 15 37 74 143 4 10 15 32 105 166 861total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 94169. Is the source water treated with aeration to remove volatile or other organic compounds?yes 4 7 5 5 9 30 0 0 0 3 2 5 0 2 2 2 9 15 50no 11 3 5 1 1 21 2 2 0 2 10 16 0 0 0 6 20 26 63did not answer 276 110 39 56 43 524 5 12 15 34 76 142 4 8 13 31 106 162 828total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 94170. Is the source water treated with air stripping towers to remove volatile or other organic compounds?yes 1 1 2 5 6 15 0 0 0 2 0 2 1 0 0 0 0 1 18no 11 3 5 1 2 22 2 2 0 2 12 18 0 0 0 7 23 30 70did not answer 279 116 42 56 45 538 5 12 15 35 76 143 3 10 15 32 112 172 853total 291 120 49 62 53 575 7 14 15 39 88 163 4 10 15 39 135 203 941

Appendix 1. Summary of ancillary information from respondents to mail-in questionnaire provided to community water systems participating in the Random Survey–Continued[Data from 941 of 954 participating community water systems that returned a response; VSM = very small (less than 500 people served); SM = small (501 to 3,300 people served); 

MED = medium (3,301 to 10,000 people served); LRG = large (10,001 to 50,000 people served); VLRG = very large (more than 50,000 people served); --, not applicable; >, greater than; <, less than]

Question

Source-water type and size of community water system

TOTAL Ground water Rivers Reservoirs

VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL VSM SM MED LRG VLRG TOTAL
66 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through October 23, 2000, for the Random Survey, by type of source water and size of community water system [Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than] Volatile organic compound Statistic Type of source water Size of community water system All sources Ground water Surface water River Reservoir Very small Small Medium Large Very Large Acrylonitrile Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 tert-Amyl methyl ether Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 2 2 0 0 0 1 0 0 1 0 Detection frequency 0.21 0.34 0 0 0 0.33 0 0 0.70 0 Min. concentration 0.21 0.21 <0.2 <0.2 <0.2 0.31 <0.2 <0.2 0.21 <0.2 Max. concentration 0.31 0.31 <0.2 <0.2 <0.2 0.31 <0.2 <0.2 0.21 <0.2 Benzene Number of samples 953 578 375 171 204 303 147 80 142 281 Number of detects 3 2 1 0 1 0 0 0 1 2 Detection frequency 0.31 0.34 0.27 0 0.49 0 0 0 0.7 0.7 Min. concentration 0.22 0.75 0.22 <0.2 0.22 <0.2 <0.2 <0.2 3.0 0.22 Max. concentration 3.0 3.0 0.22 <0.2 0.22 <0.2 <0.2 <0.2 3.0 0.75 Bromobenzene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Bromochloromethane Number of samples 953 579 374 170 204 304 147 80 142 280

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2
Appendix 2 67

Bromodichloromethane Number of samples 953 578 375 171 204 303 147 80 142 281

Number of detects 61 34 27 13 14 22 8 4 9 18Detection frequency 6.4 5.9 7.2 7.6 6.9 7.3 5.4 5.0 6.3 6.4Min. concentration 0.20 0.20 0.25 0.39 0.25 0.22 0.21 0.20 0.23 0.25Max. concentration 26 7.4 26 26 24 7.4 26 24 3.9 15

Bromoform Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 32 27 5 2 3 17 6 5 1 3Detection frequency 3.4 4.7 1.3 1.2 1.5 5.6 4.1 6.2 0.7 1.1Min. concentration 0.21 0.21 0.23 0.53 0.23 0.21 0.30 0.23 5.8 0.33Max. concentration 49 49 3.5 3.5 0.62 49 3.5 6.0 5.8 2.4

Bromomethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 2 1 1 1 0 1 0 0 0 1Detection frequency 0.21 0.17 0.27 0.58 0 0.33 0 0 0 0.36Min. concentration 0.22 6.4 0.22 0.22 <0.2 6.4 <0.2 <0.2 <0.2 0.22Max. concentration 6.4 6.4 0.22 0.22 <0.2 6.4 <0.2 <0.2 <0.2 0.22

n-Butylbenzene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 1 1 0 0 0 1 0 0 0 0Detection frequency 0.10 0.17 0 0 0 0.33 0 0 0 0Min. concentration 0.21 0.21 <0.2 <0.2 <0.2 0.21 <0.2 <0.2 <0.2 <0.2Max. concentration 0.21 0.21 <0.2 <0.2 <0.2 0.21 <0.2 <0.2 <0.2 <0.2

sec-Butylbenzene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
68 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey tert-Butylbenzene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Carbon tetrachloride Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 7 5 2 1 1 2 2 0 1 2 Detection frequency 0.73 0.86 0.53 0.58 0.49 0.66 1.4 0 0.7 0.71 Min. concentration 0.25 0.38 0.25 0.43 0.25 0.47 0.38 <0.2 0.43 0.25 Max. concentration 1.8 1.8 0.43 0.43 0.25 1.2 0.39 <0.2 0.43 1.8 Chlorobenzene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 1 1 0 0 0 0 0 0 0 1 Detection frequency 0.10 0.17 0 0 0 0 0 0 0 0.36 Min. concentration 1.6 1.6 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 1.6 Max. concentration 1.6 1.6 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 1.6 Chlorodibromomethane Number of samples 953 578 375 171 204 303 147 80 142 281 Number of detects 52 35 17 8 9 25 5 4 6 12 Detection frequency 5.5 6.1 4.5 4.7 4.4 8.2 3.4 5.0 4.2 4.3 Min. concentration 0.21 0.21 0.22 0.25 0.22 0.21 0.30 0.48 0.22 0.25 Max. concentration 20 9.4 20 20 8.9 9.4 20 8.9 2.3 4.2 Chloroethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 1 1 0 0 0 1 0 0 0 0Detection frequency 0.10 0.17 0 0 0 0.33 0 0 0 0Min. concentration 2.6 2.6 <0.2 <0.2 <0.2 2.6 <0.2 <0.2 <0.2 <0.2Max. concentration 2.6 2.6 <0.2 <0.2 <0.2 2.6 <0.2 <0.2 <0.2 <0.2

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
Appendix 2 69

Chloroform Number of samples 946 575 371 168 203 302 144 79 140 281

Number of detects 120 68 52 27 25 40 16 11 16 37Detection frequency 13 12 14 16 12 13 11 14 11 13Min. concentration 0.20 0.21 0.20 0.20 0.21 0.21 0.23 0.21 0.23 0.20Max. concentration 85 22 85 34 85 22 24 35 34 85

Chloromethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 3 3 0 0 0 2 0 0 0 1Detection frequency 0.31 0.52 0 0 0 0.66 0 0 0 0.36Min. concentration 0.20 0.20 <0.2 <0.2 <0.2 0.20 <0.2 <0.2 <0.2 0.69Max. concentration 0.69 0.69 <0.2 <0.2 <0.2 0.40 <0.2 <0.2 <0.2 0.69

2-Chlorotoluene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

4-Chlorotoluene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

Dibromomethane Number of samples 920 562 358 163 195 295 145 77 140 263

Number of detects 2 2 0 0 0 1 1 0 0 0Detection frequency 0.22 0.36 0 0 0 0.34 0.69 0 0 0Min. concentration 0.33 0.33 <0.2 <0.2 <0.2 0.33 0.75 <0.2 <0.2 <0.2Max. concentration 0.75 0.75 <0.2 <0.2 <0.2 0.33 0.75 <0.2 <0.2 <0.2

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
70 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey 1,2-Dichlorobenzene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 1 1 0 0 0 0 0 0 0 1 Detection frequency 0.10 0.17 0 0 0 0 0 0 0 0.36 Min. concentration 0.37 0.37 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.37 Max. concentration 0.37 0.37 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.37 1,3-Dichlorobenzene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 1,4-Dichlorobenzene Number of samples 953 579 374 171 203 304 147 80 141 281 Number of detects 3 1 2 1 1 0 0 0 0 3 Detection frequency 0.31 0.17 0.53 0.58 0.49 0 0 0 0 1.1 Min. concentration 0.22 0.25 0.22 0.22 0.36 <0.2 <0.2 <0.2 <0.2 0.22 Max. concentration 0.36 0.25 0.36 0.22 0.36 <0.2 <0.2 <0.2 <0.2 0.36 Dichlorodifluoromethane Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 4 4 0 0 0 1 0 0 0 3 Detection frequency 0.42 0.69 0 0 0 0.33 0 0 0 1.1 Min. concentration 1.1 1.1 <0.2 <0.2 <0.2 18 <0.2 <0.2 <0.2 1.1 Max. concentration 18 18 <0.2 <0.2 <0.2 18 <0.2 <0.2 <0.2 7.5 1,1-Dichloroethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 11 11 0 0 0 2 0 2 2 5Detection frequency 1.2 1.9 0 0 0 0.66 0 2.5 1.4 1.8Min. concentration 0.21 0.21 <0.2 <0.2 <0.2 0.21 <0.2 1.95 0.31 0.29Max. concentration 10 10 <0.2 <0.2 <0.2 0.22 <0.2 10 0.38 5.3

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
Appendix 2 71

1,2-Dichloroethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 3 3 0 0 0 1 0 1 0 1Detection frequency 0.31 0.52 0 0 0 0.33 0 1.2 0 0.36Min. concentration 0.27 0.27 <0.2 <0.2 <0.2 0.27 <0.2 0.48 <0.2 0.65Max. concentration 0.65 0.65 <0.2 <0.2 <0.2 0.27 <0.2 0.48 <0.2 0.65

1,1-Dichloroethene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 8 8 0 0 0 1 0 2 1 4Detection frequency 0.84 1.4 0 0 0 0.33 0 2.5 0.7 1.4Min. concentration 0.22 0.22 <0.2 <0.2 <0.2 23 <0.2 2.9 0.22 0.27Max. concentration 23 23 <0.2 <0.2 <0.2 23 <0.2 2.9 0.22 20

cis-1,2-Dichloroethene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 12 11 1 1 0 0 1 3 2 6Detection frequency 1.3 1.9 0.27 0.58 0 0 0.68 3.8 1.4 2.1Min. concentration 0.33 0.33 0.93 0.93 <0.2 <0.2 0.51 0.33 0.93 0.38Max. concentration 14 14 0.93 0.93 <0.2 <0.2 0.51 2.1 1.3 14

trans-1,2-Dichloroethene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

1,2-Dichloropropane Number of samples 919 561 358 163 195 295 144 77 140 263

Number of detects 1 1 0 0 0 0 0 1 0 0Detection frequency 0.11 0.18 0 0 0 0 0 1.3 0 0Min. concentration 0.47 0.47 <0.2 <0.2 <0.2 <0.2 <0.2 0.47 <0.2 <0.2Max. concentration 0.47 0.47 <0.2 <0.2 <0.2 <0.2 <0.2 0.47 <0.2 <0.2

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
72 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey 1,3-Dichloropropane Number of samples 942 569 373 170 203 302 143 80 138 279 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 2,2-Dichloropropane Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 1,1-Dichloropropene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 cis-1,3-Dichloropropene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 trans-1,3-Dichloropropene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
Appendix 2 73

Diisopropyl ether Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 2 2 0 0 0 1 0 0 0 1Detection frequency 0.21 0.34 0 0 0 0.33 0 0 0 0.36Min. concentration 0.23 0.23 <0.2 <0.2 <0.2 1.7 <0.2 <0.2 <0.2 0.23Max. concentration 1.7 1.7 <0.2 <0.2 <0.2 1.7 <0.2 <0.2 <0.2 0.23

Ethylbenzene Number of samples 939 566 373 170 203 297 143 78 141 280

Number of detects 5 3 2 0 2 1 1 2 0 1Detection frequency 0.53 0.53 0.54 0 0.98 0.34 0.70 2.6 0 0.36Min. concentration 0.23 0.23 0.26 <0.2 0.26 0.42 0.23 0.26 <0.2 0.63Max. concentration 1.0 0.63 1.0 <0.2 1.0 0.42 0.23 1.0 <0.2 0.63

Ethyl tert-butyl ether Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 1 1 0 0 0 1 0 0 0 0Detection frequency 0.10 0.17 0 0 0 0.33 0 0 0 0Min. concentration 0.25 0.25 <0.2 <0.2 <0.2 0.25 <0.2 <0.2 <0.2 <0.2Max. concentration 0.25 0.25 <0.2 <0.2 <0.2 0.25 <0.2 <0.2 <0.2 <0.2

Hexachlorobutadiene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

Hexachloroethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
74 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey Isopropylbenzene Number of samples 947 573 374 170 204 302 145 78 142 280 Number of detects 2 1 1 0 1 1 0 1 0 0 Detection frequency 0.21 0.17 0.27 0 0.49 0.33 0 1.3 0 0 Min. concentration 0.37 0.38 0.37 <0.2 0.37 0.38 <0.2 0.37 <0.2 <0.2 Max. concentration 0.38 0.38 0.37 <0.2 0.37 0.38 <0.2 0.37 <0.2 <0.2

p-Isopropyltoluene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

Methylene chloride Number of samples 952 577 375 171 204 303 147 79 142 281

Number of detects 2 1 1 1 0 0 1 1 0 0Detection frequency 0.21 0.17 0.27 0.58 0 0 0.68 1.27 0 0Min. concentration 1.6 1.6 2.6 2.6 <0.2 <0.2 1.6 2.6 <0.2 <0.2Max. concentration 2.6 1.6 2.6 2.6 <0.2 <0.2 1.6 2.6 <0.2 <0.2

Methyl ethyl ketone Number of samples 952 577 375 171 204 304 147 79 142 281

Number of detects 5 2 3 1 2 2 0 1 0 2Detection frequency 0.53 0.35 0.80 0.98 0.58 0.66 0 1.3 0 0.71Min. concentration 2.3 3.4 0.66 120 2.3 3.4 <2.0 2.3 <2.0 5.7Max. concentration 120 5.8 120 120 9.1 9.1 <2.0 2.3 <2.0 120

Methyl tert-butyl ether Number of samples 934 571 363 165 198 301 145 79 138 271

Number of detects 81 31 50 24 26 15 4 3 15 44Detection frequency 8.7 5.4 14 14 13 5.0 2.8 3.8 11 16Min. concentration 0.20 0.20 0.20 0.20 0.2 0.21 0.32 0.20 0.20 0.20Max. concentration 20 6.3 20 1.2 20 1.6 1.4 0.94 2.2 20 

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
Appendix 2 75

Naphthalene Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 2 1 1 1 0 0 1 0 0 1Detection frequency 0.21 0.17 0.27 0.58 0 0 0.68 0 0 0.36Min. concentration 0.22 0.22 1.2 1.2 <0.2 <0.2 0.22 <0.2 <0.2 1.2Max. concentration 1.2 0.22 1.2 1.2 <0.2 <0.2 0.22 <0.2 <0.2 1.2

n-Propylbenzene Number of samples 953 579 374 170 204 304 147 80 142 280

Number of detects 1 0 1 0 1 0 0 1 0 0Detection frequency 0.10 0 0.27 0 0.58 0 0 1.2 0 0Min. concentration 0.21 <0.2 0.21 <0.2 0.21 <0.2 <0.2 0.21 <0.2 <0.2Max. concentration 0.21 <0.2 0.21 <0.2 0.21 <0.2 <0.2 0.21 <0.2 <0.2

Styrene Number of samples 933 562 371 169 202 293 142 78 141 279

Number of detects 5 2 3 1 2 2 0 2 0 1Detection frequency 0.54 0.36 0.81 0.59 0.99 0.68 0 2.6 0 0.36Min. concentration 0.21 0.21 0.41 2.3 0.41 0.21 <0.2 0.41 <0.2 0.83Max. concentration 2.3 0.83 2.3 2.3 0.97 2.3 <0.2 0.97 <0.2 0.83

1,1,1,2-Tetrachloroethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

1,1,2,2-Tetrachloroethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
76 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey Tetrachloroethene Number of samples 952 577 375 171 204 303 147 80 142 280 Number of detects 27 24 3 3 0 3 4 3 4 13 Detection frequency 2.8 4.2 0.80 1.8 0 0.99 2.7 3.8 2.8 4.6 Min. concentration 0.2 0.2 0.29 0.29 <0.2 0.21 0.2 0.77 0.38 0.22 Max. concentration 36 36 5.5 5.5 <0.2 2.8 19 36 5.5 34 Toluene Number of samples 931 562 369 169 200 296 140 77 139 279 Number of detects 10 3 7 5 2 2 0 1 2 5 Detection frequency 1.1 0.53 1.9 3.0 1.0 0.68 0 1.3 1.4 1.8 Min. concentration 0.20 1.1 0.20 0.20 0.52 1.2 <0.2 1.0 0.20 0.20 Max. concentration 4.2 4.2 1.0 0.45 1.0 4.2 <0.2 1.0 0.27 1.1 1,2,3-Trichlorobenzene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 1,2,4-Trichlorobenzene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 1,1,1-Trichloroethane Number of samples 953 578 375 171 204 303 147 80 142 281

Number of detects 10 10 0 0 0 1 1 3 3 2Detection frequency 1.0 1.7 0 0 0 0.33 0.68 3.8 2.1 0.71Min. concentration 0.21 0.21 <0.2 <0.2 <0.2 6.9 13 0.26 0.21 1.4Max. concentration 13 13 <0.2 <0.2 <0.2 6.9 13 10 6.8 7.6

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
Appendix 2 77

1,1,2-Trichloroethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 0 0 0 0 0 0 0 0 0 0Detection frequency 0 0 0 0 0 0 0 0 0 0Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2

Trichloroethene Number of samples 951 576 375 171 204 303 147 79 142 280

Number of detects 22 19 3 3 0 1 4 2 5 10Detection frequency 2.3 3.3 0.80 1.8 0 0.33 2.7 2.5 3.5 3.6Min. concentration 0.23 0.23 0.31 0.31 <0.2 1.6 0.53 4.2 0.59 0.23Max. concentration 170 170 2.0 2.0 <0.2 1.6 1.9 18 8.6 170

Trichlorofluoromethane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 5 5 0 0 0 1 0 1 0 3Detection frequency 0.52 0.86 0 0 0 0.33 0 1.2 0 1.1Min. concentration 0.24 0.24 <0.2 <0.2 <0.2 0.24 <0.2 0.42 <0.2 0.92Max. concentration 1.3 1.3 <0.2 <0.2 <0.2 0.24 <0.2 0.42 <0.2 1.3

1,2,3-Trichloropropane Number of samples 954 579 375 171 204 304 147 80 142 281

Number of detects 1 1 0 0 0 0 0 1 0 0Detection frequency 0.10 0.17 0 0 0 0 0 1.2 0 0Min. concentration 0.31 0.31 <0.2 <0.2 <0.2 <0.2 <0.2 0.31 <0.2 <0.2Max. concentration 0.31 0.31 <0.2 <0.2 <0.2 <0.2 <0.2 0.31 <0.2 <0.2

1,1,2-Trichloro-1,2,2-

trifluoroethane

Number of samples 954 579 375 171 204 304 147 80 142 281Number of detects 1 1 0 0 0 0 0 0 0 1Detection frequency 0.10 0.17 0 0 0 0 0 0 0 0.36Min. concentration 0.91 0.91 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.91Max. concentration 0.91 0.91 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 0.91

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
78 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey 1,2,4-Trimethylbenzene Number of samples 945 571 374 170 204 300 145 79 141 280 Number of detects 4 1 3 2 1 0 1 0 1 2 Detection frequency 0.42 0.18 0.80 1.2 0.49 0 0.69 0 0.71 0.71 Min. concentration 0.36 0.46 0.36 0.43 0.36 <0.2 0.36 <0.2 0.43 0.46 Max. concentration 0.77 0.46 0.77 0.77 0.36 <0.2 0.36 <0.2 0.43 0.77 1,3,5-Trimethylbenzene Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Vinyl bromide Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 0 0 0 0 0 0 0 0 0 0 Detection frequency 0 0 0 0 0 0 0 0 0 0 Min. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Max. concentration <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 Vinyl chloride Number of samples 954 579 375 171 204 304 147 80 142 281 Number of detects 1 1 0 0 0 0 0 0 0 1 Detection frequency 0.10 0.17 0 0 0 0 0 0 0 0.36 Min. concentration 3.2 3.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 3.2 Max. concentration 3.2 3.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 <0.2 3.2

o-Xylene Number of samples 938 566 372 170 202 298 143 78 140 279

Number of detects 6 4 2 0 2 2 1 2 0 1Detection frequency 0.64 0.71 0.54 0 0.99 0.67 0.70 2.6 0 0.36Min. concentration 0.26 0.26 0.45 <0.2 0.45 0.36 0.26 0.45 <0.2 0.91Max. concentration 1.4 0.91 1.4 <0.2 1.4 0.44 0.26 1.4 <0.2 0.91

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
Appendix 2 79

m-, p-Xylene Number of samples 934 564 370 168 202 296 143 78 138 279

Number of detects 7 4 3 1 2 2 1 2 1 1Detection frequency 0.75 0.71 0.81 0.60 0.99 0.68 0.70 2.6 0.72 0.36Min. concentration 0.33 0.33 0.35 0.35 0.71 0.33 0.90 0.71 0.35 1.6Max. concentration 2.5 1.6 2.5 0.35 2.5 0.51 0.90 2.5 0.35 1.6

Appendix 2. Frequency of detection and concentrations of volatile organic compounds in 954 source-water samples collected from May 3, 1999, through 

October 23, 2000, for the Random Survey, by type of source water and size of community water system–Continued

[Detection frequency is percent of source-water samples with volatile organic compound concentrations equal to or greater than the minimum reporting level (MRL); MRL, 0.2 μg/L (micrograms per liter) 

for all compounds except methyl ethyl ketone which was 2.0 μg/L; Min, minimum; Max, maximum; <, less than]

Volatile organic 

compound Statistic

Type of source water Size of community water system

All 

sources

Ground

water

Surface

water River Reservoir Very small Small Medium Large Very Large
80 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

 Appendix 3. Co-occurrence of volatile organic compounds (VOCs) in source-water samples for the Random Survey 

with VOC detections

[Co-occurrence is calculated as the percentage of samples with detections of the compound specified by row beneath the heading “Volatile organic compounds” that also had detections of the compound specified beneath the column heading “Co-occurrence, in percent”, for example, 33 percent (20 samples) 

of the 61 source-water samples that contained bromodichloromethane also contained bromoform; values are shown in bold when co-occurrence equaled or 

exceeded 20 percent and there were 10 or more detections of the compound specified by row; --, not applicable; ND, no detections of compound specified in 

the column heading]

Volatile organic 

compound 

(number of detections)

Co-occurrence, in percent

Benzene

Bromodichloromethane

Bromoform Bromomethane

n-Butylbenzene

Carbon 

tetrachloride

Chlorobenzene

Benzene (3) -- 0 0 0 0 0 0

Bromodichloromethane (61) 0 -- 33 1.6 1.6 4.9 0

Bromoform (32) 0 62 -- 3.1 3.1 0 0

Bromomethane (2) 0 50 50 -- 0 0 0

n-Butylbenzene (1) 0 100 100 0 -- 0 0

Carbon tetrachloride (7) 0 43 0 0 0 -- 0

Chlorobenzene (1) 0 0 0 0 0 0 --

Chlorodibromomethane (52) 0 86 50 1.9 1.9 5.8 0

Chloroethane (1) 0 100 100 100 0 0 0

Chloroform (120) 0.8 43 14 0.8 0 3.3 0.8

Chloromethane (3) 0 33 0 0 0 0 33

Dibromomethane (2) 0 100 100 50 0 0 0

1,2-Dichlorobenzene (1) 0 0 0 0 0 0 100

1,4-Dichlorobenzene (3) 0 0 0 0 0 0 33

Dichlorodifluoromethane (4) 0 0 0 0 0 0 25

1,1-Dichloroethane (11) 9.1 9.1 18 0 0 0 9.1

1,2-Dichloroethane (3) 0 0 0 0 0 0 33

1,1-Dichloroethene (8) 0 0 0 0 0 0 12

cis-1,2-Dichloroethene (12) 0 8.3 0 0 0 8.3 8.3

1,2-Dichloropropane (1) 0 0 0 0 0 0 0

Diisopropyl ether (2) 0 0 0 0 0 0 50

Ethylbenzene (5) 0 0 0 0 0 0 0

Ethyl tert-butyl ether (1) 0 0 0 0 0 0 0

Isopropylbenzene (2) 0 0 0 0 0 0 0

Methylene chloride (2) 0 0 0 0 0 0 0

Methyl ethyl ketone (5) 0 0 0 0 0 0 0

Methyl tert-butyl ether (81) 2.5 7.4 3.7 0 1.2 1.2 1.2

Naphthalene (2) 0 0 0 0 0 0 0

n-Propylbenzene (1) 0 0 0 0 0 0 0

Styrene (5) 0 0 0 0 0 0 0

tert-Amyl methyl ether (2) 0 0 0 0 0 0 0

Tetrachloroethene (27) 3.7 3.7 3.7 0 0 0 3.7

Toluene (10) 10 0 0 0 0 0 0

1,1,1-Trichloroethane (10) 0 10 0 0 0 0 10

Trichloroethene (22) 0 4.6 4.6 0 0 0 4.6

Trichlorofluoromethane (5) 0 0 0 0 0 0 20

1,2,3-Trichloropropane (1) 0 0 0 0 0 0 0

1,1,2-Trichloro-1,2,2-

trifluoroethane (1)

0 100 0 0 0 100 0

1,2,4-Trimethylbenzene (4) 0 0 0 0 0 0 0

Vinyl chloride (1) 0 0 0 0 0 0 100

o-Xylene (6) 0 0 0 0 0 0 0

m-, p-Xylene (7) 0 0 0 0 0 0 0
Appendix 3 81

Appendix 3. Co-occurrence of volatile organic compounds (VOCs) in source-water samples for the Random Survey with 

VOC detections—Continued

Volatile organic 

compound (number of 

detections)

Co-occurrence, in percent

Chlorodibromomethane

Chloroethane Chloroform ChloromethaneDibromomethane

1,2-

Dichlorobenzene

1,4-

Dichlorobenzene

Benzene (3) 0 0 33 0 0 0 0

Bromodichloromethane (61) 74 1.6 85 1.6 3.4 0 0

Bromoform (32) 81 3.1 53 0 6.2 0 0

Bromomethane (2) 50 50 50 0 50 0 0

n-Butylbenzene (1) 100 0 100 0 0 0 0

Carbon tetrachloride (7) 43 0 57 0 0 0 0

Chlorobenzene (1) 0 0 100 100 ND 100 100

Chlorodibromomethane (52) -- 1.9 71 1.9 4.0 0 0

Chloroethane (1) 100 -- 100 0 100 0 0

Chloroform (120) 31 0.8 -- 2.5 1.7 0.8 1.7

Chloromethane (3) 33 0 100 -- 0 33.3 33

Dibromomethane (2) 100 50 100 0 -- 0 0

1,2-Dichlorobenzene (1) 0 0 100 100 ND -- 100

1,4-Dichlorobenzene (3) 0 0 67 33 0 33 --

Dichlorodifluoromethane (4) 0 0 50 25 0 0 25

1,1-Dichloroethane (11) 9.1 0 54 9.1 0 9.1 9.1

1,2-Dichloroethane (3) 0 0 67 33 0 33 33

1,1-Dichloroethene (8) 0 0 38 12 0 12 12

cis-1,2-Dichloroethene (12) 8.3 0 25 8.3 0 8.3 8.3

1,2-Dichloropropane (1) 0 0 100 0 0 0 0

Diisopropyl ether (2) 0 0 50 50 0 50 50

Ethylbenzene (5) 0 0 20 0 0 0 0

Ethyl tert-butyl ether (1) 0 0 0 0 0 0 0

Isopropylbenzene (2) 0 0 50 0 0 0 0

Methylene chloride (2) 0 0 0 0 0 0 0

Methyl ethyl ketone (5) 0 0 20 0 0 0 0

Methyl tert-butyl ether (81) 6.2 0 19 1.2 0 1.2 1.2

Naphthalene (2) 0 0 0 0 0 0 0

n-Propylbenzene (1) 0 0 100 0 0 0 0

Styrene (5) 0 0 20 0 0 0 0

tert-Amyl methyl ether (2) 0 0 0 0 0 0 0

Tetrachloroethene (27) 3.7 0 18 3.7 0 3.7 3.7

Toluene (10) 0 0 10 0 0 0 0

1,1,1-Trichloroethane (10) 0 0 50 10 0 10 10

Trichloroethene (22) 0 0 18 4.6 0 4.6 4.6

Trichlorofluoromethane (5) 0 0 20 20 0 20 20

1,2,3-Trichloropropane (1) 0 0 100 0 0 0 0

1,1,2-Trichloro-1,2,2-

trifluoroethane (1)

100 0 100 0 0 0 0

1,2,4-Trimethylbenzene (4) 0 0 0 0 0 0 0

Vinyl chloride (1) 0 0 100 100 ND 100 100

o-Xylene (6) 0 0 17 0 0 0 0

m-, p-Xylene (7) 0 0 14 0 0 0 0
82 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Appendix 3. Co-occurrence of volatile organic compounds (VOCs) in source-water samples for the Random Survey with 

VOC detections—Continued

Volatile organic 

compound (number of 

detections)

Co-occurrence, in percent

Dichlorodifluoromethane1,1-

Dichloroethane

1,2-

Dichloroethane

1,1-

Dichloroethene

cis-1,2-

Dichloroethene

1,2-

Dichloropropane

Diisopropyl

ether

Benzene (3) 0 33 0 0 0 0 0

Bromodichloromethane (61) 0 1.6 0 0 1.6 0 0

Bromoform (32) 0 6.2 0 0 0 0 0

Bromomethane (2) 0 0 0 0 0 0 0

n-Butylbenzene (1) 0 0 0 0 0 0 0

Carbon tetrachloride (7) 0 0 0 0 14 0 0

Chlorobenzene (1) 100 100 100 100 100 ND 100

Chlorodibromomethane (52) 0 1.9 0 0 1.9 0 0

Chloroethane (1) 0 0 0 0 0 0 0

Chloroform (120) 1.7 5 1.7 2.5 2.5 0.9 0.8

Chloromethane (3) 33 33 33 33 33 0 33

Dibromomethane (2) 0 0 0 0 0 0 0

1,2-Dichlorobenzene (1) 100 100 0 100 100 ND 100

1,4-Dichlorobenzene (3) 33 33 33 33 33 0 33

Dichlorodifluoromethane (4) -- 25 25 25 75 0 25

1,1-Dichloroethane (11) 18 -- 18 46 46 10 9.1

1,2-Dichloroethane (3) 33 67 -- 67 67 50 33

1,1-Dichloroethene (8) 12 62 25 -- 50 17 12

cis-1,2-Dichloroethene (12) 25 42 17 33 -- 8.3 8.3

1,2-Dichloropropane (1) 0 100 100 100 100 -- 0

Diisopropyl ether (2) 50 50 50 50 50 0 --

Ethylbenzene (5) 0 0 0 0 0 0 0

Ethyl tert-butyl ether (1) 0 0 0 0 0 0 0

Isopropylbenzene (2) 0 0 0 0 0 0 0

Methylene chloride (2) 0 0 0 0 0 0 0

Methyl ethyl ketone (5) 0 0 0 0 0 0 0

Methyl tert-butyl ether (81) 1.2 4.9 1.2 2.5 4.9 0 2.5

Naphthalene (2) 0 0 0 0 0 0 0

n-Propylbenzene (1) 0 0 0 0 0 0 0

Styrene (5) 0 0 0 0 0 0 0

tert-Amyl methyl ether (2) 0 0 0 0 0 0 50

Tetrachloroethene (27) 11 18 7.4 11 37 3.8 3.7

Toluene (10) 0 0 0 0 0 0 0

1,1,1-Trichloroethane (10) 10 50 20 50 40 11 10

Trichloroethene (22) 14 23 9.1 14 46 4.8 4.6

Trichlorofluoromethane (5) 40 60 20 40 60 0 20

1,2,3-Trichloropropane (1) 0 100 100 100 100 100 0

1,1,2-Trichloro-1,2,2-

trifluoroethane (1)

0 0 0 0 100 0 0

1,2,4-Trimethylbenzene (4) 0 0 0 0 0 0 0

Vinyl chloride (1) 100 100 100 100 100 ND 100

o-Xylene (6) 0 0 0 0 0 0 0

m-, p-Xylene (7) 0 0 0 0 0 0 0
Appendix 3 83

Appendix 3. Co-occurrence of volatile organic compounds (VOCs) in source-water samples for the Random Survey with 

VOC detections—Continued

Volatile organic 

compound (number of 

detections)

Co-occurrence, in percent

Ethylbenzene

Ethyl 

tert-butyl

ether

IsopropylbenzeneMethylene

chloride

Methyl ethyl

ketone

Methyl 

tert-butyl

ether

Naphthalene

Benzene (3) 0 0 0 0 0 100 0

Bromodichloromethane (61) 0 0 0 0 0 10 0

Bromoform (32) 0 0 0 0 0 9.4 0

Bromomethane (2) 0 0 0 0 0 0 0

n-Butylbenzene (1) 0 0 0 0 0 100 0

Carbon tetrachloride (7) 0 0 0 0 0 14 0

Chlorobenzene (1) 0 0 0 0 0 100 0

Chlorodibromomethane (52) 0 0 0 0 0 9.8 0

Chloroethane (1) 0 0 0 0 ND 0 0

Chloroform (120) 0.8 0 0.8 0 0.8 13 0

Chloromethane (3) 0 0 0 0 0 33 0

Dibromomethane (2) 0 0 0 0 0 0 0

1,2-Dichlorobenzene (1) 0 0 0 0 0 100 0

1,4-Dichlorobenzene (3) 0 0 0 0 0 33 0

Dichlorodifluoromethane (4) 0 0 0 0 0 25 0

1,1-Dichloroethane (11) 0 0 0 0 0 36 0

1,2-Dichloroethane (3) 0 0 0 0 0 33 0

1,1-Dichloroethene (8) 0 0 0 0 0 25 0

cis-1,2-Dichloroethene (12) 0 0 0 0 0 33 0

1,2-Dichloropropane (1) 0 0 0 0 0 0 0

Diisopropyl ether (2) 0 0 0 0 0 100 0

Ethylbenzene (5) -- 0 20 0 40 20 0

Ethyl tert-butyl ether (1) ND -- 0 0 0 100 0

Isopropylbenzene (2) 50 0 -- 0 50 50 0

Methylene chloride (2) 0 0 0 -- 0 0 50

Methyl ethyl ketone (5) 50 0 25 0 -- 20 0

Methyl tert-butyl ether (81) 1.2 1.2 1.2 0 1.2 -- 0

Naphthalene (2) 0 0 0 50 0 0 --

n-Propylbenzene (1) 100 0 100 0 100 100 0

Styrene (5) 80 0 20 0 40 40 0

tert-Amyl methyl ether (2) 0 0 0 0 0 100 0

Tetrachloroethene (27) 0 0 0 0 0 26 0

Toluene (10) 10 0 0 0 10 40 0

1,1,1-Trichloroethane (10) 0 0 0 0 0 30 0

Trichloroethene (22) 0 0 0 0 0 14 0

Trichlorofluoromethane (5) 0 0 0 0 0 20 0

1,2,3-Trichloropropane (1) 0 0 0 0 0 0 0

1,1,2-Trichloro-1,2,2-

trifluoroethane (1)

0 0 0 0 0 100 0

1,2,4-Trimethylbenzene (4) 33 0 0 0 25 0 0

Vinyl chloride (1) 0 0 0 0 0 100 0

o-Xylene (6) 100 17 17 0 33 33 0

m-, p-Xylene (7) 71 0 14 0 29 14 0
84 National Survey of MTBE and Other VOCs in Drinking-Water Sources: Results of the Random Survey

Appendix 3. Co-occurrence of volatile organic compounds (VOCs) in source-water samples for the Random Survey with 

VOC detections—Continued

Volatile organic 

compound (number of 

detections)

Co-occurrence, in percent

n-Propylbenzene Styrene tert-Amyl

methyl ether

Tetrachloroethene Toluene

1,1,1-

Trichloroethane

Trichloroethene

Benzene (3) 0 0 0 33 33 0 0

Bromodichloromethane (61) 0 0 0 1.6 0 1.6 1.6

Bromoform (32) 0 0 0 3.1 0 0 3.1

Bromomethane (2) 0 0 0 0 0 0 0

n-Butylbenzene (1) 0 0 0 0 0 0 0

Carbon tetrachloride (7) 0 0 0 0 0 0 0

Chlorobenzene (1) 0 0 0 100 0 100 100

Chlorodibromomethane (52) 0 0 0 1.9 0 0 0

Chloroethane (1) 0 0 0 0 0 0 0

Chloroform (120) 0.8 0.8 0 4.2 0.8 4.2 3.3

Chloromethane (3) 0 0 0 33 0 33 33

Dibromomethane (2) 0 0 0 0 0 0 0

1,2-Dichlorobenzene (1) 0 0 0 100 0 100 100

1,4-Dichlorobenzene (3) 0 0 0 33 0 33 33

Dichlorodifluoromethane (4) 0 0 0 75 0 25 75

1,1-Dichloroethane (11) 0 0 0 46 0 46 50

1,2-Dichloroethane (3) 0 0 0 67 0 67 67

1,1-Dichloroethene (8) 0 0 0 38 0 62 38

cis-1,2-Dichloroethene (12) 0 0 0 83 0 33 91

1,2-Dichloropropane (1) 0 0 0 100 0 100 100

Diisopropyl ether (2) 0 0 50 50 0 50 50

Ethylbenzene (5) 20 80 0 0 25 0 0

Ethyl tert-butyl ether (1) 0 ND 0 0 ND 0 0

Isopropylbenzene (2) 50 100 0 0 0 0 0

Methylene chloride (2) 0 0 0 0 0 0 0

Methyl ethyl ketone (5) 20 50 0 0 33 0 0

Methyl tert-butyl ether (81) 1.2 2.5 2.5 8.6 5.1 3.7 3.7

Naphthalene (2) 0 0 0 0 0 0 0

n-Propylbenzene (1) -- 100 0 0 ND 0 0

Styrene (5) 20 -- 0 0 25 0 0

tert-Amyl methyl ether (2) 0 0 -- 0 0 0 0

Tetrachloroethene (27) 0 0 0 -- 0 15 56

Toluene (10) 0 10 0 0 -- 0 0

1,1,1-Trichloroethane (10) 0 0 0 40 0 -- 56

Trichloroethene (22) 0 0 0 68 0 23 --

Trichlorofluoromethane (5) 0 0 0 80 0 40 60

1,2,3-Trichloropropane (1) 0 0 0 100 0 100 100

1,1,2-Trichloro-1,2,2-

trifluoroethane (1)

0 0 0 0 0 0 0

1,2,4-Trimethylbenzene (4) 0 33 0 0 67 0 0

Vinyl chloride (1) 0 0 0 100 0 100 100

o-Xylene (6) 17 80 0 0 25 0 0

m-, p-Xylene (7) 14 57 0 0 33 0 0
Appendix 3 85

Appendix 3. Co-occurrence of volatile organic compounds (VOCs) in source-water samples for the Random Survey with 

VOC detections—Continued

Volatile organic 

compound (number of 

detections)

Co-occurrence, in percent

Trichlorofluoromethane1,2,3-

Trichloropropane

1,1,2-Trichloro1,2,2-trifluoroethane1,2,4-Trimethyl

benzene

Vinyl 

chloride o-Xylene m-, pXylene

Benzene (3) 0 0 0 0 0 0 0

Bromodichloromethane (61) 0 0 1.6 0 0 0 0

Bromoform (32) 0 0 0 0 0 0 0

Bromomethane (2) 0 0 0 0 0 0 0

n-Butylbenzene (1) 0 0 0 0 0 0 0

Carbon tetrachloride (7) 0 0 14 0 0 0 0

Chlorobenzene (1) 100 0 0 0 100 0 0

Chlorodibromomethane (52) 0 0 1.9 0 0 0 0

Chloroethane (1) 0 0 0 0 0 0 0

Chloroform (120) 0.8 0.8 0.8 0 0.8 0.8 0.8

Chloromethane (3) 33 0 0 0 33 0 0

Dibromomethane (2) 0 0 0 0 0 0 0

1,2-Dichlorobenzene (1) 100 0 0 0 100 0 0

1,4-Dichlorobenzene (3) 33 0 0 0 33 0 0

Dichlorodifluoromethane (4) 50 0 0 0 25 0 0

1,1-Dichloroethane (11) 27 9.1 0 0 9.1 0 0

1,2-Dichloroethane (3) 33 33 0 0 33 0 0

1,1-Dichloroethene (8) 25 12 0 0 12 0 0

cis-1,2-Dichloroethene (12) 25 8.3 8.3 0 8.3 0 0

1,2-Dichloropropane (1) 0 100 0 0 0 0 0

Diisopropyl ether (2) 50 0 0 0 50 0 0

Ethylbenzene (5) 0 0 0 20 0 100 100

Ethyl tert-butyl ether (1) 0 0 0 0 0 100 ND

Isopropylbenzene (2) 0 0 0 0 0 50 50

Methylene chloride (2) 0 0 0 0 0 0 0

Methyl ethyl ketone (5) 0 0 0 25 0 50 50

Methyl tert-butyl ether (81) 1.2 0 1.2 0 1.2 2.5 1.3

Naphthalene (2) 0 0 0 0 0 0 0

n-Propylbenzene (1) 0 0 0 0 0 100 100

Styrene (5) 0 0 0 20 0 80 80

tert-Amyl methyl ether (2) 0 0 0 0 0 0 0

Tetrachloroethene (27) 15 3.7 0 0 3.7 0 0

Toluene (10) 0 0 0 20 0 11 20

1,1,1-Trichloroethane (10) 20 10 0 0 10 0 0

Trichloroethene (22) 14 4.6 0 0 4.6 0 0

Trichlorofluoromethane (5) -- 0 0 0 20 0 0

1,2,3-Trichloropropane (1) 0 -- 0 0 0 0 0

1,1,2-Trichloro-1,2,2-

trifluoroethane (1)

0 0 -- 0 0 0 0

1,2,4-Trimethylbenzene (4) 0 0 0 -- 0 33 67

Vinyl chloride (1) 100 0 0 0 -- 0 0

o-Xylene (6) 0 0 0 17 0 -- 100

m-, p-Xylene (7) 0 0 0 29 0 71 --